[Feature]: Add Success Message to Newsletter Form

[akshay0611]

Problem:
The current newsletter form lacks feedback for users after they successfully subscribe, which may leave them uncertain about whether their submission was successful.

Proposed Solution:

• Add a success message or button that appears after the user submits their email.
• Use JavaScript to handle the form submission and display the success message dynamically.

Expected Outcome:
A newsletter form that provides clear feedback to users upon successful subscription, improving user experience and engagement.