Sarc 368 loki connect

[nurbal]

This PR adds an opentelemetry logging handler that sends logs to a loki endpoint.
Related settings added in the logging section of the settings JSON file:

    "logging": {
        "log_level": "INFO",
        "OTLP_endpoint": "http://path.to.loki.endpoint/otlp/v1/logs",
        "service_name": "sarc"
    },

[nurbal]

J'ai renoncé à tester de bout en bout le logger vers loki, de part la difficulté à utiliser logging au sein d'un test (pytest intercepte le logging, et j'ai tout essayé pour désactiver cela sans succès). Au lieu de cela, un test plus restreint du logging handler de opentelemetry vers loki est mis en place, avec un httpserver pour mocker le endpoint.

[bouthilx]

The problem now is that verbose_level will always override the config log level even if set with the command line. A solution would be that verbose_level is set to None when not specified in cmdline.

[nurbal]

Damn, you're right.
Fixed in ab430fe
Command-line has priority if specified (-v or -vv); config-file log level is used otherwise.