[5.1] Convert mod_syndicate to service provider

[joomlaweby]

Summary of Changes

Converts the syndicate link site module to service provider.

Testing Instructions

1. Make sure you have site module mod_syndicate published
2. Make sure you have RSS Feed link enabled in Articles component configuration (Integration tab)
3. You should see module output on articles listing menu items - Category blog, Featured articles...
4. You should not see module output on other menu item types - Single Article, other components...

Actual result BEFORE applying this Pull Request

Module works as expected

Expected result AFTER applying this Pull Request

Module works same way as before applying pull request

Link to documentations

Please select:

• Documentation link for docs.joomla.org:

• No documentation changes for docs.joomla.org needed

• Pull Request link for manual.joomla.org:

• No documentation changes for manual.joomla.org needed

[fgsw]

I have tested this item ✅ successfully on fdcea5c

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[viocassel]

I have tested this item ✅ successfully on fdcea5c

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[richard67]

RTC

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[LadySolveig]

Thank you @joomlaweby and also for testing @fgsw @viocassel