The JSON formatter used to rely on services making their logging calls
and passing the context there. A call it expted would be
LOG.debug("Some message", context=context)
This would end up in the "extra" section of the logging record. This is
not usually the case, as projects don't always pass the context on that
call. This also applies to the Fluent formatter which is based on the
JSON one.
For the JSON formatter, we already are getting the context from the
record. So lets use that if no context was provided in the record's
'extra' section. Finally, this places the context in its own section,
which is named 'context'.
Closes-Bug: #1730329
Depends-On: I2b245c1665c3587be3c476b803122788d186e5d5
Change-Id: I765dae17d2ecadce1672f16e432e748d5233acf8
1b012d0fc6