Implement Success Message for Newsletter Subscription with Auto-dismiss After 4 Seconds

[akshay0611]

Currently, when a user subscribes to the newsletter, there is no success message displayed upon submission. The task is to add a success message that appears when a user submits their email, thanking them for subscribing and advising them to check their inbox for the latest updates. The message should automatically disappear after 4 seconds.

The following changes should be made:

1. Add a success message under the form.
2. Implement JavaScript functionality to show the success message upon form submission.
3. Hide the success message after 4 seconds.