[Enhancement]: Add Success Message to Newsletter Form

[akshay0611]

Problem:
The current newsletter form lacks feedback for users after they submit their email, which may leave them unsure if their submission was successful.

Proposed Solution:

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

Expected Outcome:
A newsletter form that provides immediate feedback to users, improving their experience and encouraging further engagement.