Add safeguards to deter people from making any changes to commit message formats

[twarit-waikar]

1. Add a comment here that says the changing the commit message format is a significant change which needs to be evaluated by code owners. The blast radius of changing this format needs to be contained in a single location.
   

   p4-fusion/p4-fusion/git_api.cc

   Line 204 in 3ee4824

   std::string commitMsg = cl + " - " + desc + "\n[p4-fusion: depot-paths = \"" + depotPath.substr(0, depotPath.size() - 3) + "\": change = " + cl + "]";

2. Add tests the try to detect if a change in the commit message format has been made and if it is a valid change.