Destroy file attachments when file is deleted, or object is deleted

Summary:
Adds file attachment deletion logics:

• PhabricatorFile: delete the attachment if file is deleted
• destruction engine extension: delete attachment if object is deleted
• SQL patch: delete existing leftover attachments from deleted files

To apply the cleanup, as usual, run:

./bin/storage upgrade

This cleanup may take some time, proportionally to the size of these tables:

phabricator_file.file
phabricator_file.file_attachment

Just as an indication: the storage upgrade, in a Phorge with file count 1.3M rows and file_attachment consisting in 9K rows, it may delete 170K rows in less than 1 second on average hardware.

Closes T15110

Test Plan:
Apply the patch, run ./bin/storage/upgrade:

• no "Unknown Object" in any "Referenced Files" curtain of any object.

Have phd daemon running.

Upload file, attach the file to a task, delete the file from the web interface:

• no "Unknown Object" in "Referenced Files" curtain of that task.
• the query SELECT * FROM file_attachment WHERE filePHID = '<file phid>' returns empty result

Upload file, attach the file to a task, delete the task from the ./bin/remove destroy workflow:

• the query SELECT * FROM file_attachment WHERE objectPHID = '<task phid>' returns empty result

Reviewers: O1 Blessed Committers, avivey, valerio.bozzolan

Reviewed By: O1 Blessed Committers, avivey, valerio.bozzolan

Subscribers: Ekubischta, speck, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Tags: #files

Maniphest Tasks: T15110

Differential Revision: https://we.phorge.it/D25051