feat: Add LinksTo Property

[octfx]

This PR adds a new Links to property that records pages to which a page links.

The namespaces where this property is allowed to be active can be configured using $sespgLinksToEnabledNamespaces.

Example:
$sespgLinksToEnabledNamespaces = [ 10, 838 ]; would activate the Links to property only on Template and Module namespaces.

This PR includes:

• Tests (unit)
• CI build passed

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 54.28571% with 16 lines in your changes missing coverage. Please review.

Project coverage is 90.19%. Comparing base (b5af401) to head (3fc38c6).
Report is 101 commits behind head on master.

Files with missing lines	Patch %	Lines
...rc/PropertyAnnotators/LinksToPropertyAnnotator.php	54.28%	16 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #216      +/-   ##
============================================
- Coverage     91.42%   90.19%   -1.24%     
- Complexity      357      368      +11     
============================================
  Files            35       36       +1     
  Lines          1015     1050      +35     
============================================
+ Hits            928      947      +19     
- Misses           87      103      +16     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[alistair3149]

@JeroenDeDauw Hi there! It has been a while since the CR is addressed and would you be able to take a look at the patch again?

[jaideraf]

@alistair3149 or @octfx please add documentation of the new feature at least here: https://github.com/SemanticMediaWiki/SemanticExtraSpecialProperties/blob/master/docs/configuration.md

[alistair3149]

PR opened at #245 for documentation