ci: workflows: pin python dependencies

Pin python dependencies to hashes and cleanup/unify python setup steps in
various workflows.

We now have one dependency file containing all requirements for github
actions that is managed centrally with hashes. No direct pip installs
are needed in workflow files and everything shall go via the
requirements file.

Pinning to specific version and hashes helps with preventing supply
chain attacks.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>