cmd/gopherbot: move "ping-early-issues" task to relui

[dmitshur]

Pinging issues with "early-in-cycle" is a task that we do once every 6 months, after the development of a new major Go version starts. Right now it's implemented as a task in gopherbot that needs to be explicitly run with -only-run=ping-early-issues flag (and provide a URL of the reopening announcement via the openTreeURLs map).

Now that we have relui, this task can move there. Not only is it slightly easier to trigger the task via a web UI, it also eliminates the need of setting up credentials for running goperbot on a local workstation. Having it in relui also opens future opportunities like eventually making it a part of a larger "reopen tree for development" workflow, etc.

This is the tracking issue for moving the task to relui. To avoid bringing in the maintner dependency into relui, I'll also rewrite it to use GitHub API v4 (GraphQL) instead and use it as an opportunity to see what that looks like.

CC @golang/release.

[gopherbot]

Change https://go.dev/cl/473160 mentions this issue: cmd/relui: add a "ping early-in-cycle issues" workflow

[gopherbot]

Change https://go.dev/cl/473159 mentions this issue: cmd/gopherbot: replace maintner with GitHub API v4 in ping-early-issues

[dmitshur]

This is done and worked to ping early issues in the Go 1.22 milestone recently.

This was also a bit of an exercise to see if GitHub's GraphQL API can help when moving away from maintner as a dependency. My conclusion is that it helps a bit, but using maintner (if it works) is still so much nicer and simpler.

There's a harmless TODO in code to decide "if it's worth moving the GraphQL query/mutation". I had the idea of possibly moving the query into GitHubClientInterface, but that really means moving the entire task's implementation there. I don't think it's worth it now, but can revisit this later.