Move IncomingEmail and ServiceDesk to Email namespace

What does this MR do and why?

Address movement of namespace mentioned in #381505 (closed)

There is no logic change, just a namespace change.

This MR seems big but the changes are just namespace addition to class files and usage of those classes.

Screenshots or screen recordings

NA

How to set up and validate locally

1. Nothing to verify except everything should work as expected.
2. Pipeline should be green.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #381505 (closed)