configure rules to merge rabbitmq_identity_info

[mmueller-rs]

This closes #1855

Note to reviewers: remember to look at the commits in this PR and consider if they can be squashed

Summary Of Changes

If the same rabbitmq_identity_info (same pod, same cluster, etc.) is exported twice, only one of the values is used.

Additional Context

When using the default ServiceMonitor from https://github.com/rabbitmq/cluster-operator/blob/main/observability/prometheus/monitors/rabbitmq-servicemonitor.yml, multiple Metrics-Endpoints are scraped that partly return the same value.

Local Testing

It can be tested by applying the files to a test-cluster:

  - https://raw.githubusercontent.com/mmueller-rs/cluster-operator/fix-prometheus-rules-for-duplicate-metrics/observability/prometheus/rules/rabbitmq/cluster-alarms.yml
  - https://raw.githubusercontent.com/mmueller-rs/cluster-operator/fix-prometheus-rules-for-duplicate-metrics/observability/prometheus/rules/rabbitmq/container-restarts.yml
  - https://raw.githubusercontent.com/mmueller-rs/cluster-operator/fix-prometheus-rules-for-duplicate-metrics/observability/prometheus/rules/rabbitmq/file-descriptors-near-limit.yml
  - https://raw.githubusercontent.com/mmueller-rs/cluster-operator/fix-prometheus-rules-for-duplicate-metrics/observability/prometheus/rules/rabbitmq/high-connection-churn.yml
  - https://raw.githubusercontent.com/mmueller-rs/cluster-operator/fix-prometheus-rules-for-duplicate-metrics/observability/prometheus/rules/rabbitmq/insufficient-established-erlang-distribution-links.yml
  - https://raw.githubusercontent.com/mmueller-rs/cluster-operator/fix-prometheus-rules-for-duplicate-metrics/observability/prometheus/rules/rabbitmq/low-disk-watermark-predicted.yml
  - https://raw.githubusercontent.com/mmueller-rs/cluster-operator/fix-prometheus-rules-for-duplicate-metrics/observability/prometheus/rules/rabbitmq/no-majority-of-nodes-ready.yml
  - https://raw.githubusercontent.com/mmueller-rs/cluster-operator/fix-prometheus-rules-for-duplicate-metrics/observability/prometheus/rules/rabbitmq/persistent-volume-missing.yml
  - https://raw.githubusercontent.com/mmueller-rs/cluster-operator/fix-prometheus-rules-for-duplicate-metrics/observability/prometheus/rules/rabbitmq/recording-rules.yml
  - https://raw.githubusercontent.com/mmueller-rs/cluster-operator/fix-prometheus-rules-for-duplicate-metrics/observability/prometheus/rules/rabbitmq/tcp-sockets-near-limit.yml
  - https://raw.githubusercontent.com/mmueller-rs/cluster-operator/fix-prometheus-rules-for-duplicate-metrics/observability/prometheus/rules/rabbitmq/unroutable-messages.yml

Please ensure you run the unit, integration and system tests before approving the PR.

To run the unit and integration tests:

$ make unit-tests integration-tests

You will need to target a k8s cluster and have the operator deployed for running the system tests.

For example, for a Kubernetes context named dev-bunny:

$ kubectx dev-bunny
$ make destroy deploy-dev
# wait for operator to be deployed
$ make system-tests