Sync with playbooks: install-go-tools, gotestsum, and dynamic versions

[lieut-data]

Summary

This brings into the starter-template a handful of changes originally introduced with Playbooks:

• an automatic install-go-tools target that manages a local, versioned copy of any go installed tools needed
• adoption of gotestsum for improved go testing semantics
• reverting the embedding of plugin.json, restoring make apply, and shifting to a dynamically generated version number based on the nearest tag.

This last point is easier explained by linking to the original PR: https://github.com/mattermost/mattermost-plugin-playbooks/pull/433, but I note that the reason I reverted embedding plugin.json is that this root file is no longer the final source of truth: rather, it's a (big) input into the final manifest that includes the dynamically generated version. Open to different approaches, but either way we don't have to care about checking in the generated manifests: they remain generated and .gitignored.

In this repository, since we have yet to tag a version, any build will result in v0.0.0+<commit hash>. Any build on a tagged version will be vX.Y.Z exactly. And any downstream commit from there would be vX.Y.Z+<short hash> until we tag a new version.

Ticket Link

None.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (376ea7e) 5.26% compared to head (0ac4026) 5.26%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #192 +/- ## ====================================== Coverage 5.26% 5.26% ====================================== Files 3 3 Lines 38 38 ====================================== Hits 2 2 Misses 36 36 ```

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