TP fix filtering on Delivery Service "Targets For" column

[shamrickus]

On the "Targets For" column in the Delivery Services table, the filtering/sorting does not work at all.

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Which Traffic Control components are affected by this PR?

• Traffic Portal

What is the best way to verify this PR?

Try to sort/filter the Targets For column on the Delivery Services page in TP, ensure it succeeds.

If this is a bugfix, which Traffic Control versions contained the bug?

• master

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)