ci(all): Skip required features if no code changed

[vbuberen]

Description

This PR adds a new workflow to skip required checks in PRs with green statuses in case some PR only touches docs, website or other non-related code. With this workflow we should have no more cases with PRs having yellow status awaiting checks to complete, like we now have in #1300, for example:

Workflow follows the guide from the official docs: https://docs.github.com/en/repositories/configuring-branches-and-merges-in-your-repository/defining-the-mergeability-of-pull-requests/troubleshooting-required-status-checks#handling-skipped-but-required-checks

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I titled the PR using Conventional Commits.
• I did not modify the CHANGELOG.md nor the pubspec.yaml files.
• All existing and new tests are passing.
• The analyzer (flutter analyze) does not report any problems on my PR.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate that with a ! in the title as explained in Conventional Commits).
• No, this is not a breaking change.

[miquelbeltran]

Very smart, thanks!