x/build/cmd/gopherbot: add command to rebase CLs

[matloob]

Hi,

I often want to make sure that a change will pass trybots once it's applied to head. It seems like the only way to do that is to rebase the change, and then run trybots. So it would be nice if we could easily rebase CLs on gerrit (we currently need the "Forge Author" permission).

[dmitshur]

I often want to make sure that a change will pass trybots once it's applied to head.

We can achieve this either by allowing rebasing, or by making trybots able to do this as part of testing. /cc @bradfitz

[agnivade]

We can achieve this either by allowing rebasing, or by making trybots able to do this as part of testing

That's #9858

[dmitshur]

Gerrit now provides an ability to rebase on behalf of the original CL author, which doesn't require Forge Author permission. See here. Can you give it a try @matloob?

Optimistically closing this, since I don't expect there's a need to add anything to gopherbot given the new native Gerrit UI.