Refactor command bot and drop rejecting non paritytech members (#7231)

Aims to 
- close #7049 
- close https://github.com/paritytech/opstooling/issues/449
- close https://github.com/paritytech/opstooling/issues/463

What's changed:
- removed is paritytech member check as required prerequisite to run a
command
- run the cmd.py script taking it from master, if someone who run this
is not a member of paritytech, and from current branch, if is a member.
That keeps the developer experience & easy testing if paritytech members
are contributing to cmd.py
- isolate the cmd job from being able to access GH App token or PR
token- currently the fmt/bench/prdoc are being run with limited
permissions scope, just to generate output, which then is uploaded to
artifacts, and then the other job which doesn't run any files from repo,
does a commit/push more securely