Provide documentation on overriding runtime config & config APIs

[tomkerkhove]

Provide documentation on overriding runtime config & config APIs.

Fixes #682
Fixes #673

[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:pr687

Want to verify the new version? Run it locally:

docker run -d -p 8999:80 --name promitor-agent-scraper-pr687 \
                         --env PROMITOR_AUTH_APPID='<azure-ad-app-id>' \
                         --env-file C:/Promitor/az-mon-auth.creds \
                         --volume C:/Promitor/metrics-declaration.yaml:/config/metrics-declaration.yaml  \
                         --volume C:/Promitor/runtime-config.yaml:/config/runtime.yaml \
                         tomkerkhove/promitor-agent-scraper-ci:pr687

You can find a CI version of our Helm chart on hub.helm.sh