ref(grouping): Add git SHA parameterization

[lobsterkatie]

It is standard git practice to abbreviate commit SHAs to 7 digits where there's no ambiguity. However, for message parameterization our current hex matching only applies to strings 8 characters and up. This therefore adds a new, separate pattern to our collection of parameterizer regexes, specifically to match git SHAs. It's similar to our hex regex, but stricter, in that the string must be exactly 7 characters, must include both a letter and a number (this will miss a few, but both words and ints are more common, so we let them win), and must only use lowercase letters, as git always does.

[shashjar]

nice