[6.2] MailTemplate should work with interface

[laoneo]

• I read the Generative AI policy and my contribution is either not created with the help of AI or is compatible with the policy and GNU/GPL 2 or later.

Summary of Changes

The MailTemplate class should work with an injected MailerInterface and not concrete implementation to be more flexible. Additionally this pr deprecates the optional parameter to be able to remove the deprecated Factory usage.

Testing Instructions

• Log in on the back end
• Got to the global configuration server tab
• Send a test mail

Actual result BEFORE applying this Pull Request

Mail is sent.

Expected result AFTER applying this Pull Request

Mail is sent.

Link to documentations

Please select:

• Documentation link for guide.joomla.org:

• No documentation changes for guide.joomla.org needed

• Pull Request link for manual.joomla.org: MailTemplate should work with interface Manual#620

• No documentation changes for manual.joomla.org needed

[CSGoat0]

I have tested this item ✅ successfully on a59506a

I followed the instructions, everything works fine.

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[exlemor]

I have tested this item ✅ successfully on a59506a

I have tested this successfully! Thanks @laoneo!

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[richard67]

RTC

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[MacJoom]

Please check