[4.2] Change tags plugin to service provider

[laoneo]

Summary of Changes

Change tags plugin to service provider. Did also some code style cleanup.

Testing Instructions

• Open the article form
• Define some tags
• Save the article

Actual result BEFORE applying this Pull Request

Tags are stored and assigned to the new article.

Expected result AFTER applying this Pull Request

Tags are stored and assigned to the new article.

[joomdonation]

I have tested this item ✅ successfully on 00fc446

Add, remove tags, batch assign tags, all still works as expected

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[alikon]

I have tested this item ✅ successfully on 00fc446

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[alikon]

RTC

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[roland-d]

Thanks everybody