Only log warning when no default aggregation is configured

[tomkerkhove]

Fixes #521

[promitor-bot]

Docker image for this PR was built and is available on Docker Hub.

You can pull it locally via the CLI:

docker pull tomkerkhove/promitor-agent-scraper-ci:pr522

Want to verify the new version? Run it locally:

docker run -d -p 8999:80 --name promitor-agent-scraper-pr522 \
                         --env PROMITOR_AUTH_APPID='<azure-ad-app-id>' \
                         --env PROMITOR_AUTH_APPKEY='<azure-ad-app-key>' \
                         --volume C:/Promitor/metrics-declaration.yaml:/config/metrics-declaration.yaml \
                         tomkerkhove/promitor-agent-scraper-ci:pr522