Traffic Ops: log a warning instead of ignoring write errors

[rawlinp]

What does this PR (Pull Request) do?

• This PR fixes Traffic Ops HTTP response write errors are ignored #5954

Which Traffic Control components are affected by this PR?

• Traffic Ops

What is the best way to verify this PR?

Ensure the TO API tests still pass. Since this logging only happens on write errors, one way to test the logging would be to set the traffic_ops_golang.request_timeout in cdn.conf to 1 and make a request to a certain endpoint which is known to take longer than 1 second to return a response. Alternatively, you could add a time.sleep(5*time.Second) into some handler and call that instead. You should see a log like the following:

WARNING: api.go:120: 2021-06-29T21:44:57.123243Z: failed to write response (method = GET, URL = /api/3.1/ping, request ID = 1, remote addr = [::1]:62136, bytes written = 0): http: Handler timeout

If this is a bug fix, what versions of Traffic Control are affected?

4.x, 5.x, master

The following criteria are ALL met by this PR

• minor logging fixes, tests didn't seem necessary
• logging fixes, no docs needed
• This PR includes an update to CHANGELOG.md
• This PR includes any and all required license headers
• This PR DOES NOT FIX A SERIOUS SECURITY VULNERABILITY (see the Apache Software Foundation's security guidelines for details)

[srijeet0406]

Changes look good.
Unit + API tests pass.
Manual testing resulted in the log line being generated.
LGTM!