Allow controlling Otel log level in different environments

This is mainly to help us suppress the verbose output on enabling
different instrumentations on startup in test environments, but
also could be generally useful. More on the PR to enable it:
open-telemetry/opentelemetry-ruby#831

config/config.yml.example

@@ -127,6 +127,7 @@ development: &default
   otel_service_name: # "pender"
   otel_resource_attributes:
     # developer.name: <DEVELOPER_NAME>
+  otel_log_level: info
 
 test:
   <<: *default
@@ -137,6 +138,7 @@ test:
   storage_medias_asset_path: 'http://localhost:9000/check-test/medias'
   otel_exporter_otlp_endpoint:
   otel_exporter_otlp_headers:
+  otel_log_level: error
   airbrake_host:
 
 production: