A Llama and Llama Stack Powered Email Agent

[jeffxtang]

What does this PR do?

This is a Llama Stack port of the Email Agent app that shows how to build a practical email agent app powered by Llama 3.1 8B and Llama Stack, using Llama Stack's powerful and easy to use custom tool and agent APIs.

Closes # (issue)

Feature/Issue validation/testing/test plan

Please describe the tests that you ran to verify your changes and relevant result summary. Provide instructions so it can be reproduced.
Please also list any relevant details for your test configuration or test plan.

• Test A
  Logs for Test A

• Test B
  Logs for Test B

Sources

Please link relevant resources if necessary.

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline,
  Pull Request section?
• Was this discussed/approved via a Github issue? Please add a link
  to it if that's the case.
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests?

Thanks for contributing 🎉!

[mattf]

fyi, the source agent was moved to https://github.com/meta-llama/llama-cookbook/tree/main/end-to-end-use-cases/email_agent