ParseAndEnhance used to be:
- Try to parse line as a syslog, extracting the log itself and other
fields from syslog format
- If that succeeds, try to parse the log as either a Kayvee log or
an RDS slow query log.
- Combine all these fields, and add on some "derived"
fields (container_task|env|app).
- Not a syslog => error
Now it will be:
- Try to parse line as a syslog, same as before, including the
Kayvee/RDS part
- If syslog parsing failed, try to parse as a Fluent log and extract
some fields from the Fluent format (the log, timestamp, etc)
- If that succeeds, try to parse the log itself as a Kayvee log.
- Combine Kayvee fields (if found) and derived fields)
- If BOTH formats fields, it is an error.
The decoding makes a lot of assumptions:
- The names of the log field and timestamp field (even though,
theoretically, they are customizable in the fluentbit config.
- The timestamp format (again)
- The format of the Task Definition name (or at least part of it)
- All fluentbit logs should have hostname set to `aws-fargate`.
Perhaps these can be relaxed if necessary. They could probably be
replaced by some kind of config. As there is currently no config I
wanted to keep things simple as possible. If we need to re-evaluate
(for example if we start getting JSON logs that don't want to use the
same handling for container_task|env|app) we can reevaluate.
type is a really generally name. sometimes, it is used in other
libraries or various output as a valid field name. let's not make it a
reserved keyword that gets overriden by type == Kayvee
Previously, this would result in a log line failing to extracting any
dimensions because
```golang
dimensions.([]string)
```
would fail because
```golang
reflect.TypeOf(dimensions)
```
was `[]interface{}`.
