bug: Cannot recognise bash-style arguments in Dockerfile

[ShauryaAg]

devcontainer cli is unable to parse bash-style arguments, that is, arguments of type ${arg1:+"something"}

For example:
When using the below Dockerfile

ARG cloud
FROM ${cloud:+"my.ecr.repo/"}myimage:tag

The output after parsing should be, if the value cloud ARG is set:

FROM my.exr.repo/myimage:tag

and otherwise should be:

FROM myimage:tag

However,
devcontainer cli throws an error that it cannot parse the above mentioned Dockerfile

[11 ms] @devcontainers/cli 0.25.2. Node.js v16.14.2. darwin 21.2.0 arm64.
[469 ms] Parsed version '+' for input 'docker.io/library/1:+' failed validation.
Error: Command failed: docker inspect --type image 1:+
    at Aoe (/Users/shaurya/.vscode/extensions/ms-vscode-remote.remote-containers-0.266.1/dist/spec-node/devContainersSpecCLI.js:70182:9)
    at uT (/Users/shaurya/.vscode/extensions/ms-vscode-remote.remote-containers-0.266.1/dist/spec-node/devContainersSpecCLI.js:70175:11)
    at async Poe (/Users/shaurya/.vscode/extensions/ms-vscode-remote.remote-containers-0.266.1/dist/spec-node/devContainersSpecCLI.js:70543:34)
    at async Zf (/Users/shaurya/.vscode/extensions/ms-vscode-remote.remote-containers-0.266.1/dist/spec-node/devContainersSpecCLI.js:70597:9)
    at async aue (/Users/shaurya/.vscode/extensions/ms-vscode-remote.remote-containers-0.266.1/dist/spec-node/devContainersSpecCLI.js:72760:13)
    at async oue (/Users/shaurya/.vscode/extensions/ms-vscode-remote.remote-containers-0.266.1/dist/spec-node/devContainersSpecCLI.js:72747:9)
{"outcome":"error","message":"Command failed: docker inspect --type image 1:+","description":"An error occurred setting up the container."}

In the above run, the value of cloud argument was set to 1, hence it outputted 1:+, which is not the expected result.

devcontainer cli version: 0.25.2

Reference:

• https://docs.docker.com/engine/reference/builder/#environment-replacement

[ShauryaAg]

Hey, @joshspicer I have submitted a PR for the reported issue, could you please review it?