Feat: add backend to the newsletter page

[AyushSharma72]

Describe the feature

currently there is no backend in the newsletter when anyone click the website just reloads

i will add a api and a custom template when the user subscribe he will receive an email
like this

Add ScreenShots

i will create a custom template for buddytrail

Record

• I agree to follow this project's Code of Conduct
• I'm a GSSOC'24 contributor
• I want to work on this issue

[github-actions]

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[github-actions]

Thanks for creating the issue in BuddyTrail!
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