TO API uses non-RFC3339 date/time strings

[ocket8888]

I'm submitting a ...

• other

Traffic Control components affected ...

• Traffic Ops
• unknown

Current behavior:

Traffic Ops API responses frequently return our custom format for date/times: YYYY-MM-DD hh:mm:ss-ZZ ("2006-01-02 15:04:05-07" is the actual Go format string).

Expected behavior:

The Traffic Ops API (in the latest API version, where the behavior is breakable) should respond with RFC3339-format date strings.

Minimal reproduction of the problem with instructions:

Make most any TO API request.

[ocket8888]

In practice we use UTC everywhere of which I know, but this time format is not capable of representing all time zones, should that ever come up.