Add --prometheus_addr command line parameter

[tgxworld]

This commit adds support for the --prometheus_addr command line
parameter to allow binding the Prometheus metrics server on a different
host address.

Reviewer notes

Helm Chart: If your new feature introduces settings consider adding those to the Helm chart README.md and values.yaml

I'm not quite sure how to do this so would like to get some help here if possible.

[jertel]

Kubernetes typically handles the services on its own, so we'll skip adding the address param to the Helm chart.

Since there are no existing tests for the prometheus port we'll skip that as well.

[tgxworld]

Since there are no existing tests for the prometheus port we'll skip that as well.

Do you know if there is an existing way to set up elastalert2 and elasticsearch in the development environment for testing purposes? I noticed that there were no existing tests as well but would like to at least be able to test the changes by hand locally.

[jertel]

In the docs it shows how to run a local environment directly with Python. I suggest creating a virtual environment (venv) first to avoid collisions with other Python apps.

[tgxworld]

@jertel I manage to test my changes locally by hand using the following steps:

1. docker network create test
2. docker run --rm --name elasticsearch --net test -p 9200:9200 -p 9300:9300 -e "discovery.type=single-node" -e "xpack.security.http.ssl.enabled=false" -e "xpack.security.enabled=false" elasticsearch:8.17.1
3. Git checkout my changes and build the image locally: docker build . --file Dockerfile --tag elastalert2
4. mkdir /tmp/rules
5. cp ./examples/config.yaml.example ./examples/config.yaml
6. Change the value of es_host: in ./example/config.yaml to elasticsearch
7. docker run --rm -it --net test -p 9979:9979 -v ./examples/config.yaml:/opt/elastalert/config.yaml -v /tmp/rules:/opt/elastalert/rules elastalert2:latest --prometheus_port 9979 --prometheus_addr "::"

[tgxworld]

@jertel Thank you for reviewing