Allow to configure self-diagnostics log verbosity via ENV variable

[LumirH]

We are using application insights within the Kubernetes environment.
App insights JAR and applicationinsights.json are bundled in the standard docker image and provide good "default" values for all microservices. When we start the docker image, we "personalize" the config through the env variables (set APPLICATIONINSIGHTS_ROLE_NAME, etc...)

One thing I miss is the ability to override the self-diagnostics logging level using ENV variable -- I often need to temporarily increase the verbosity to troubleshoot app insights behavior. At the moment, I need to "replace applicationinsights.json" to do it.

{
"selfDiagnostics": {
"destination": "file+console",
"level": "DEBUG",
}

This is not convenient.
It would be much easier to just set APPLICATIONINSIGHTS_SELFDIAGNOSTICS_LEVEL=DEBUG....