Make metrics server port configurable

[douglas-c]

Adds a flag to the controller to support configuring a non-default port for the metrics collection.

This resolves an issue where running secretgen-controller with hostNetwork=true may lead to port conflicts on the node.

Fixes #509

Testing Done:

• Built and ensured passing unit tests locally
• Deployed in a Kind cluster and loaded Docker image onto cluster
• Edited Deployment to add new container arg: -metrics-bind-address=:8093
• Confirmed new secretgen-controller Pod logged the change:

...
{"level":"info","ts":"2023-12-07T21:19:22Z","logger":"controller-runtime.metrics","msg":"Metrics server is starting to listen","addr":":8093"}
{"level":"info","ts":"2023-12-07T21:19:22Z","logger":"sg.entrypoint","msg":"setting up controllers"}
{"level":"info","ts":"2023-12-07T21:19:22Z","logger":"sg.entrypoint","msg":"starting manager"}
{"level":"info","ts":"2023-12-07T21:19:22Z","msg":"Starting server","path":"/metrics","kind":"metrics","addr":"[::]:8093"}
...