lint(track_config): check concept directory names are in config

[ErikSchierboom]

With this PR, configlet lint now produces an error if there is a subdirectory in the concepts directory of a track that does not have a corresponding entry in the track-level config.json file.

The implementation is similar to the exercise-based check.

See exercism/rust#1363 (comment) CC @coriolinus

[ee7]

Currently, this PR produces the below diff to the output of configlet lint, per-track:

csharp

+`./concepts` contains a directory named `enumerables`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+`./concepts` contains a directory named `lambdas`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+`./concepts` contains a directory named `math-operators`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+Configlet detected at least one problem.
+For more information on resolving the problems, please see the documentation:
+https://github.com/exercism/docs/blob/main/building/configlet/lint.md

go

+`./concepts` contains a directory named `anonymous-functions`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+`./concepts` contains a directory named `application-timing`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+`./concepts` contains a directory named `bytes`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+`./concepts` contains a directory named `channels`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+`./concepts` contains a directory named `conditionals`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+`./concepts` contains a directory named `context`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+`./concepts` contains a directory named `defer`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+`./concepts` contains a directory named `duration`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+`./concepts` contains a directory named `empty-interface`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+`./concepts` contains a directory named `errors-handling`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+`./concepts` contains a directory named `goroutines`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+`./concepts` contains a directory named `mutex`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+`./concepts` contains a directory named `panic`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+`./concepts` contains a directory named `recover`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+`./concepts` contains a directory named `reflection`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+`./concepts` contains a directory named `select`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+`./concepts` contains a directory named `variables`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+Configlet detected at least one problem.
+For more information on resolving the problems, please see the documentation:
+https://github.com/exercism/docs/blob/main/building/configlet/lint.md

julia

+`./concepts` contains a directory named `arithmetic-operators`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+`./concepts` contains a directory named `boolean-expressions`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+`./concepts` contains a directory named `integer-equality`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+`./concepts` contains a directory named `iterator-protocol`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+`./concepts` contains a directory named `nothingness`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+`./concepts` contains a directory named `pairs`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+`./concepts` contains a directory named `vectors`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+

kotlin

+`./concepts` contains a directory named `booleans`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+Configlet detected at least one problem.
+For more information on resolving the problems, please see the documentation:
+https://github.com/exercism/docs/blob/main/building/configlet/lint.md

rust

+`./concepts` contains a directory named `string-vs-str`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+

swift

+`./concepts` contains a directory named `constants-and-variables`, which is not a `slug` in the concepts array. Please add the concept to that array:
+./config.json
+
+Configlet detected at least one problem.
+For more information on resolving the problems, please see the documentation:
+https://github.com/exercism/docs/blob/main/building/configlet/lint.md

[ee7]

Looks good to me.

I'd have merged already, but there's an unusual long delay in the Windows build. I already tried restarting once.

Approved merging with this commit message body:

With this commit, `configlet lint` now produces an error if there is
a subdirectory in the `concepts` directory of a track that does not have
a corresponding entry in the track-level `config.json` file.

which is just the body of 7be9163 with whitespace changes.

[ErikSchierboom]

Done. Thanks for the review.