Update and Handle messageType for GIFs as MediaEmbed

[meKushdeepSingh]

Problem:

• The Send API returns an error when trying to send a GIF as a reply message.

Diagnose:

• The GIF message type has been deprecated in the latest Push SDK and is no longer supported.

Solution:

• Update the message type to MediaEmbed and implement the corresponding changes in web UI in the Push SDK to ensure compatibility with current standards.