Add Last Updated field to Traffic Portal

[shamrickus]

This PR adds the Last Updated field to every DS form in Traffic Portal (tpv2 already has them).

---

Which Traffic Control components are affected by this PR?

• Traffic Portal

What is the best way to verify this PR?

Verify the last updated field is present on each type of Delivery Service and is correct in Traffic Portal.

PR submission checklist

• [x] This PR has tests
• [x] This PR has documentation
• [x] This PR has a CHANGELOG.md entry
• [x] This PR DOES NOT FIX A SERIOUS SECURITY VULNERABILITY (see the Apache Software Foundation's security guidelines for details)