Change Logging Level from a Config File

[bprobert97]

Is your feature request related to a problem? Please describe.
Following on from #282 - we can now set the LabThings logging level for debug using the cli. As @rwb27 notes, in the future it may make sense to put debug into the config file as well as having it in cli.

Describe the solution you'd like
Add debug to config file options, using 'from_config()'

Describe alternatives you've considered
We currrently have a cli flag. This would be retained in addition to adding debug in the config file.

[rwb27]

I'm in favour. Lots of servers allow logging levels to be specified in a config file, I think it makes sense and will be useful.