detectLevelFromLogLine does not cover all cases

[sofielanduyts]

The func detectLevelFromLogLine is not fully complete. (loki/pkg/distibutor/distributor.go)
For example, log lines with WARN .... will not be handled as level warning.

Removing the colon would include all cases.

This creates inconsistency with grafana as well.

Even though there is no detected_level, it does get the color orange.

[camrossi]

Having a similar issue as well, where my level is called "cleared" that is probably not super standard either :)

I did mention it in #12645 as I am also wondering how to handle this in the "right" way

[jafnhaar]

Somehow all log lines with WARN handled as errors on my loki

[rlex]

It will be nice if we can map them in loki config, since there is many variations. warning/WARN, error/ERR, there is also numerical severity in some apps.