Add expiry option for inactive exempt wikis

[Reception123]

In order to complete the transition away from using a manual Dormancy Policy exemption table, it's necessary to also include the option to set expiry as quite a few exemptions are given temporarily only.

Note: This patch is partially written by LLMs with adjustments and has already been tested on beta.

miraheze/ManageWiki#791 should also be merged once this is.

[codecov]

Codecov Report

❌ Patch coverage is 76.19048% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 31.35%. Comparing base (a195951) to head (b38e0eb).

Files with missing lines	Patch %	Lines
includes/Helpers/RemoteWiki.php	84.21%	3 Missing ⚠️
includes/Helpers/ManageWikiCoreModule.php	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #826      +/-   ##
============================================
+ Coverage     31.10%   31.35%   +0.24%     
- Complexity      835      842       +7     
============================================
  Files            48       48              
  Lines          3806     3827      +21     
============================================
+ Hits           1184     1200      +16     
- Misses         2622     2627       +5     

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