Allow controlling Otel log level in different environments (#295)

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

Also updates encrypted config.yml for test runs on CI with 
new test configuration keys to lower Otel log level in test

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:

config/initializers/open_telemetry.rb

@@ -1,6 +1,10 @@
 require 'pender_open_telemetry_config'
 require 'pender_open_telemetry_test_config'
 
+# Lines immediately below set any environment config that should 
+# be applied to all environments
+ENV['OTEL_LOG_LEVEL'] = PenderConfig.get('otel_log_level')
+
 unless Rails.env.test?
   Pender::OpenTelemetryConfig.new(
     PenderConfig.get('otel_exporter_otlp_endpoint'),