Ideas for PR comment-driven automation

[trask]

• /spotless - ./gradlew spotlessApply
• /rebase- merge main into the PR branch - this would be helpful for testLatestDeps fixes
• /license - ./gradlew generateLicenseReport - this would be helpful on some dependabot PRs
• /rerun - rerun failed tests, helpful for contributors who don't normally have this level of access

[mateuszrzeszutek]

Also maybe /api-diff? Would be quite useful in the SDK repo too

[trask]

Closing, as the more useful of these (spotless, license) require running gradle against PR branch changes under elevated permissions