Change some instances of "phabricator" to "phorge"

Summary:
Just a small set of replacements in locations that seem innocuous (user-facing messages, documentation, etc.)

Ref T15006

Test Plan:
Nothing should change in terms of behavior. The places where these changes were made should now say "phorge".

Example tests:

• Manage a single User and click on Delete User and see the popup
• Run a test email and check the output ./bin/mail send-test --to username
• Visit /maniphest/, shift+click on at least 1 Task, click on Bulk Edit Selected, Continue, see the popup
• See the mentioned documentation with your big eyes. Eyes do not explode \o/

Reviewers: O1 Blessed Committers, valerio.bozzolan

Reviewed By: O1 Blessed Committers, valerio.bozzolan

Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T15006

Differential Revision: https://we.phorge.it/D25473