PR migrator workflow

[RobPasMue]

After ansys/pymapdl#3878

@germa89 implemented a great workflow to port over PRs from external contributors into our repositories. Due to the usage of secrets on our side, PRs from forked repositories can't run the workflows properly.

Once a repository maintainer has reviewed the forked repo's PR, he could port it over to the main repo with this action (while continuing to provide ownership to the main author through the commit history) and allowing it to properly run (since it will have access to the secrets)

We should consider adding this PR as part of our hk-* section.

[germa89]

Just ping me when you want me to prepare the PR. :)

[MaxJPRey]

Definitely a must have. Nice work in ansys/pymapdl#3878 @germa89 .