Provide API endpoint for getting runtime configuration

[tomkerkhove]

Fixes #638

[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:pr640

Want to verify the new version? Run it locally:

docker run -d -p 8999:80 --name promitor-agent-scraper-pr640 \
                         --env PROMITOR_AUTH_APPID='<azure-ad-app-id>' \
                         --env-file C:/Promitor/az-mon-auth.creds \
                                                  --volume C:/Promitor/runtime-declaration.yaml:/config/runtime.yaml \
                                                  --volume C:/Promitor/metrics-declaration.yaml:/config/metrics-declaration.yaml \
                                                                           tomkerkhove/promitor-agent-scraper-ci:pr640

                                                                       You can find a CI version of our Helm chart on [hub.helm.sh](https://hub.helm.sh/charts/promitor/promitor-agent-scraper-ci)