perfstar branch creation gh action

[JanProvaznik]

workflow to speed up running perfstar on a PR, creates a new perf/ prefixed branch on comment by insiders. which has the PRs changes + merged main into it.

Testing

https://github.com/JanProvaznik/actiontesting - this workflow successfully creates a new perf prefixed branch on /perfstar comment

Usage

1. Someone (external/internal) creates a PR
2. member of the dotnet org or collaborator see gh docs on this repo can comment /perfstar on the PR
3. the action runs, creates a branch in the repo perf/original-pr-branch-name
4. on this new branch prefixed with perf, the internal perfstar infrastructure runs and members of the team can look at the report

[Copilot]

Copilot reviewed 1 out of 1 changed files in this pull request and generated no comments.

[maridematte]

Could you add an example on how this works? How do you trigger it and who can trigger this branch creation?

[JanProvaznik]

@maridematte I added usage to description