[Enhancement]: Add Success Message to Callback Form

[akshay0611]

Problem:
The current callback form does not provide feedback to users after they submit their email address. This can lead to confusion about whether their submission was successful.

Proposed Solution:

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

Expected Outcome:
A more user-friendly callback form that confirms successful submissions, improving the overall user experience.