ci: create Go Generate workflow

[galargh]

Resolves #47

This implements a request described in #47 (comment)

We can also specify labels, assignees, reviewers and team-reviewers for the PR if we want.

[rvagg]

👌 I think this should be OK, there may be cases where the submodule will be updated but will not generate changes, but there shouldn't be many of those. Thanks @galargh!

[lidel]

@galargh just fyi test run https://github.com/multiformats/go-multicodec/actions/runs/3267378296 has this note:

The set-output command is deprecated and will be disabled soon. Please upgrade to using Environment Files. For more information see: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/

Probably not something we need to fix asap, but it will impact all our actions, not just this one.

[galargh]

Yes, thanks for flagging. I've seen that this week. The good thing is they're unlikely to completely deprecate it any time soon since:

We are monitoring telemetry for the usage of these commands and plan to fully disable them in the future.

I created an issue for this in uCI - protocol/.github#405 - so that we get to it ahead of the February 2023 release. I'll do a sweep of all our orgs when I start working on that issue.