v2.19: Make setting logging level possible

[JakobMiksch]

• Make setting logging level possible by providing the environment variable GEOSERVER_LOG_LEVEL
• The environment variable USE_STD_OUT_LOGGING defines if logging should be done to standard out.
• It also works when a volume is mounted on the host system.
• Custom logging profiles can be used by placing them in the GeoServer data directory

[chrismayer]

Maybe it is better not to place the logging profiles directly into geoserver_data/ (geoserver_data/logs/), which is quite often used as a direct mount point. I think adding a new folder logging_profiles at root level and copying the content in the build step might be a better option.

[JakobMiksch]

@chrismayer I updated the PR - now the usage of a mounted volume works as it should be.