[Feature]: Add Success Message to Newsletter Subscription Form

[akshay0611]

Problem:
The current newsletter subscription form lacks feedback for users after they submit their email address, which can lead to confusion about whether the submission was successful.

Proposed Solution:

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

Expected Outcome:
A more user-friendly newsletter subscription form that provides clear feedback upon successful submission.