Fix json response for invalid invalidation job. Moved CHANGELOG entry

[tcfdev]

Addresses an issue discovered in testing the TO v4.0 /jobs endpoint. The validation of the incoming job was wrapping the alert and error response inside another alert and error response.

Incorrect response:

{
  "alerts": [
    {
      "text": "{\"alerts\":[{\"text\":\"deliveryService: cannot be blank.\",\"level\":\"error\"}]}\n",
      "level": "error"
    }
  ]
}

Fixed response:

{
  "alerts": [
    {
      "text": "deliveryService: cannot be blank.",
      "level": "error"
    }
  ]
}

Also moved a CHANGELOG entry for the REFETCH feature into the correct location for the CHANGELOG.

---

Which Traffic Control components are affected by this PR?

• Traffic Ops

What is the best way to verify this PR?

Run Traffic Ops and attempt to POST a new invalidation request to the /jobs endpoint. The following json will trigger a validation error, alert response:

{
	"startTime": "2021-11-05T16:24:00.370Z",
	"regex": "/path/to/some/content\\.jpg",
	"ttlHours": 24,
	"invalidationType": "REFRESH"
}

PR submission checklist

• This PR has tests - Does not have a functional aspect, only asthetic.
• This PR has documentation - No documented logic is changed, added, or deleted.
• This PR has a CHANGELOG.md entry
• This PR DOES NOT FIX A SERIOUS SECURITY VULNERABILITY (see the Apache Software Foundation's security guidelines for details)

[zrhoffman]

Also moved a CHANGELOG entry for the REFETCH feature into the correct location for the CHANGELOG.

If you put that in a separate PR, I'll merge it right away

[srijeet0406]

LGTM! Manual tests pass. API and unit tests pass.

[dneuman64]

retest this please

[zrhoffman]

retest this please

Failing due to the ATS RPM version-calculating issue fixed by #6329

[zrhoffman]

In order for CI to pass, #6328 needs to be rebased onto the apache:master branch now that the CI fix in #6329 is merged:

git remote add apache git@github.com:apache/trafficcontrol.git
git fetch apache
git rebase apache
git push your-fork your-branch --force