Build plugin

[SandersAaronD]

This is currently waiting on this pr:

grafana/plugin-actions#28

And the github action here should be changed to reference the grafana-maintained github action instead of referencing the branch from my PR. (In the past I have not done this and this has created technical debt over in grafana-llm-app).

Provided that is done, the release workflow from this action would be:

1. Push the plugin version tag to the desired commit, which will trigger the workflow
2. Go to the draft PR created by github actions and publish it
3. Manually publish the plugin on grafana.com if we want it to be downloadable from grafana.com

Steps 2. and 3. can be rolled into automation if necessary, but we don't actually need to do this to run the plugin in dev environments; we can simply use the github release.

[SandersAaronD]

This should be good now; there is unfortunately no way to test the publish to gcom step without merging it, so we may need to do a few small patches before it becomes fully end to end.

[annanay25]

LGTM (mod the pending PR in plugin-actions repo)

[SandersAaronD]

@annanay25 Wasn't sure they'd ever merge that PR, decided to copy all the code over here, should be just fine (and a lot easier to maintain over time).