Java: shutdown executor when a servlet is destroyed

[aaronforest-wf]

Story:

The executors provided to our nats servers are shutdown when the server is stopped, but the executors provided to our http servlets are not shut down when the servlet is destroyed.

Note: I only updated the FJakartaServlet to shutdown its executor service on servlet destroy. I can apply the same change to the deprecated javax FServlet if it would be valuable.

Acceptance Criteria:

• [ ] Code has been tested and results documented
• [ ] Unit tests have been updated
• [ ] Updates to documentation if necessary
• [ ] Verify and document changes to any other Messaging components
• [ ] Pull request made against the 'develop' branch, not master

Design Notes:

TODO

How To Test:

TODO

My Test Results:

TODO

Reviewers:

@Workiva/service-platform