"OCIS_TRACING_TYPE":"otlp" - value "otlp is not described in envvar descriptions

Reading that we can now use `otlp` as value for `OCIS_TRACING_TYPE`, I checked if that value is described in the envvar descriptions in master - which is not.

This value needs to be added for each service where `OCIS_TRACING_TYPE` is used.
For a list of services using that envvar see: [Global Environment Variables](https://doc.owncloud.com/ocis/next/deployment/services/env-vars-special-scope.html#global-environment-variables).

@butonic