Think about what we do with remote-apis-sdks #3614

We use this as a dependency which saved us from writing a bunch of Go code.

However now t seems to be not quite dead (just pining for the fjords) but its main user (reclient) has gone away (in favour of Siso). PRs aren't getting merged at much of a rate (e.g. bazelbuild/remote-apis-sdks#621 which I'm working around in #3613).

It has been useful for us but also is difficult to upgrade because they don't do versions, release notes or compatibility. There have also been some architectural changes to it which historically haven't been very useful to us but have needed work to update to. Fortunately this is all a bit easier to navigate these days with the tools we have available now but it is still work.

Options would be:

1. Stay as we are (pinning it and managing upgrades carefully)
2. Fork it, which would give us more control, but now we own it (although we wouldn't support it for any use other than our own)
3. Bin it and write our own replacement.

Right now we're implicitly doing #1. Logging this so we have a more explicit discussion of this pain point.