Dispose entities on unmaintained namespace, add maintenance alert, refs 4468

[mwjames]

This PR is made in reference to: #4468

This PR addresses or contains:

• The disposeOutdatedEntities.php script will check for "invalid entities" on unmaintained namespaces which may have been lingering in the object table due to a removed namespace setting where a user did not run a rebuild of the data as suggested by [0]
• Adds a maintenance alert for invalid entities by namespace

This PR includes:

• Tests (unit/integration)
• CI build passed

[0] https://www.semantic-mediawiki.org/wiki/Help:Custom_namespaces

Example

$ php maintenance/disposeOutdatedEntities.php

Semantic MediaWiki:                                             3.2.0-alpha
MediaWiki:                                                     1.35.0-alpha

--- About -----------------------------------------------------------------

This script will remove outdated entities and entities rendered invalid due
to redeclared namespace settings. It will also dispose of query link
entries from tables that no longer hold a valid entity reference in
Semantic MediaWiki.

--- Outdated entitie(s) ---------------------------------------------------

Removing outdated and invalid entities ...
   ... checking outdated entities ...                                     ✓
   ... checking invalid entities by namespace ...
       ... cleaning up entity                                   4836 (100%)
       ... removed (IDs) ...                                              1
   ... done.

Removing query links ...
   ... checking query links (invalid) ...                                 ✓
   ... checking query links (unassigned) ...                              ✓
   ... done.

[kghbln]

Documented