refactor: further cleanup

[sakulstra]

this pr assumed default branch to be changed to main and Pending-aips being pushed to main after merge

• targeting parts of what is discussed in [RFC] cleanup & simplify processes #181

This pr resolves the points

• proposal naming: the readme just sais "uppercase name" and the ci enforces this in pr validation. No more hash. In theory AIP-num prs could be renamed, but that's bit cumbersome work. Might do it in new pr.
• removing status: it's removed from templates & validation. We don't remove it from existing aip payloads as this would alter the hash.
• branching: @kartojal once this is merged default branch has to be changed and you need to push Pending-AIPs to main

What this pr does not cover is pr ipfs previews: was looking a bit into this but perhaps someone involved in aave interface ci can have a look as I didn't quite understand how pull_request vs pull_request_target stuff works.