add tag name unique per job to CLI/API; address Phil's feedback

Add partial explaining why tag, add to CLI/API

website/content/api-docs/jobs.mdx

@@ -2702,6 +2702,8 @@ WebSocket Request: /v1/job/actions-demo/action?action=weather&allocID=8614ed07-4
 
 This endpoint creates a tag for a job version.
 
+@include 'version/tag-reason.mdx'
+
 | Method | Path              | Produces           |
 | ------ | ----------------- | ------------------ |
 | `POST`  | `/v1/job/:job_id/versions/:tag_name/tag` | `application/json` |
@@ -2711,7 +2713,7 @@ This endpoint creates a tag for a job version.
 - `:job_id` `(string: <required>)` - The ID of the job. Specify `job_id` as part
   of the path.
 - `:tag_name` `(string: <required>)` - The new tag name for the
-  version specified in the payload. Specify `tag_name` as part of the path.
+  version specified in the payload. Must be unique per job. Specify `tag_name` as part of the path.
 - `Version`: `(int: <optional>)` - The job version number. If not
   specified, Nomad tags the latest version. Specify `Version` in the payload.
 - `Description`: `(string: <optional>)` - The tag description. Specify `Description` in the payload.

website/content/docs/commands/job/revert.mdx

@@ -31,10 +31,10 @@ authentication.
 nomad job revert [options] <job> <version|tag>
 ```
 
-The `job revert` command requires two inputs, the job ID and the version or tag
-of that job to revert to.  When you specify a version number, Nomad reverts the
-job to the exact version number. Alternately, when you specify a version tag,
-Nomad reverts to the version with that tag.
+The `job revert` command requires two inputs, the job ID and the version number
+or tag of that job to revert to.  When you specify a version number, Nomad
+reverts the job to the exact version number. Alternately, when you specify a
+version tag, Nomad reverts to the version with that tag.
 
 When ACLs are enabled, this command requires a token with the `submit-job`
 capability for the job's namespace. The `list-jobs` capability is required to

website/content/docs/commands/job/tag.mdx

@@ -8,6 +8,8 @@ description: |
 
 # Command: job tag
 
+@include 'version/tag-reason.mdx'
+
 Use the `job tag` command to manage tags for job versions. `job tag` has the
 following subcommands:
 
@@ -38,7 +40,7 @@ nomad job tag apply [options] <job_id>
 
 ### Apply options
 
-- `name`: Specifies the name of the tag.
+- `name`: Specifies the name of the tag. Must be unique per job.
 - `description`: If set, specifies a description for the tag.
 - `version`: If set, specifies the version of the job to tag. If not provided, Nomad tags the latest version of the job.
 

website/content/partials/version/tag-reason.mdx

@@ -0,0 +1,4 @@
+Applying a tag to a version prevents Nomad from garbage collecting that version.
+You can compare versions by tag name as well as version number.
+
+Tag names must be unique per job.