Add a hook for modifying the Special:CreateWiki form

[lihaohong6]

For the CreateWikiLoadout extension.

It's also nice to be able to add additional fields to Special:CreateWiki if similar needs arise in the future.

Only tested on localhost.

[Universal-Omega]

Just FYI Special:CreateWiki will eventually be removed and replaced with a auto-create-via-request feature in Special:RequestWiki for better log management and lookup, and tracking creations better. It should hardly ever be used in production anyway. Either way no real issues with this though, but it doesnt do all that much good for CreateWiki since that will hardly ever be used at all.

[lihaohong6]

Ah that's good to know. Would be really nice to have a unified interface for wiki creation.

This is primarily motivated by having to go through Special:RequestWiki and the AI every time a test wiki is created on beta. Wouldn't be a big deal if we don't merge this patch either.

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 32.04%. Comparing base (0de8847) to head (1be598a).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
includes/Specials/SpecialCreateWiki.php	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #813      +/-   ##
============================================
+ Coverage     31.96%   32.04%   +0.08%     
- Complexity      806      807       +1     
============================================
  Files            47       47              
  Lines          3695     3701       +6     
============================================
+ Hits           1181     1186       +5     
- Misses         2514     2515       +1     

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