Add Git Action to test for "Signed off" message on commit messages

[musamarcusso]

GitHub now has a new feature that verifies if the committer added the Signed off message in the commit message, which is a requirement in the UUV Simulator project.

The feature has been activated project wide:
https://github.com/organizations/uuvsimulator/settings/installations/9543973

This means that any pull request where the commit messages have not been created with git commit -s -m <message> will not be allowed to be merged.