Set ActionName to "Created" for PhabricatorTransactions::TYPE_CREATE

Summary:
Explicitly set "Created" as ActionName (to be used as a mail subject line vary prefix) when the transaction type is PhabricatorTransactions::TYPE_CREATE to avoid falling back to a generic "Updated" prefix.

Closes T15865

Test Plan: Either create a new task and check the mail subject line prefix (if you have a mail setup in your Phorge instance), or use the debug patch in P45 and check the order of action strengths.

Reviewers: O1 Blessed Committers, valerio.bozzolan

Reviewed By: O1 Blessed Committers, valerio.bozzolan

Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T15865

Differential Revision: https://we.phorge.it/D25732