docs: add Thunderdome docs for releases

[guseggert]

The Thunderdome testing will probably need additional documentation as we refine the process, and it's complicated enough that putting it inline in the release checklist is a bit much, so I've split it into its own file.

[BigLep]

Thanks for writing Gus. Generally seems good. I think we're missing a step on how we collect and share the results.

I think keeping an experiment log like @iand did in https://www.notion.so/pl-strflt/ce2d1bd56f3541028d960d3711465659 makes sense. I am game for us putting the results there, but the expectation should be that as part of the release process we're updating the release issue with a link to the experiment where someone can see the grafana dashboard and our analysis (and any accompanying slack threads).

[guseggert]

the expectation should be that as part of the release process we're updating the release issue with a link to the experiment where someone can see the grafana dashboard and our analysis (and any accompanying slack threads).

This makes sense, just know that only PL folks can see the experiment dashboards (hosted Grafana dashboards can't be public).

[iand]

We could host a prometheus+grafana in the thunderdome account just for collecting results and showing them publicly

[BigLep]

Looks good - thanks @guseggert