Add enableFeatures field to MonitoringStack prometheusConfig

[emilarnesen]

Summary

Adds a new enableFeatures field to the MonitoringStack prometheusConfig spec, allowing users to enable Prometheus feature flags (e.g. exemplar-storage, native-histograms) on Prometheus instances managed by the observability-operator.

The underlying CommonPrometheusFields in the prometheus-operator already supports EnableFeatures []EnableFeature, but the MonitoringStack CRD did not expose it. This PR wires it through.

Resolves #995

Changes

• pkg/apis/monitoring/v1alpha1/types.go — Added EnableFeatures []string field to PrometheusConfig with kubebuilder validation
• pkg/controllers/monitoring/monitoring-stack/components.go — Wire EnableFeatures through to the Prometheus CR via a toEnableFeatures() conversion function ([]string → []monv1.EnableFeature)
• pkg/apis/monitoring/v1alpha1/zz_generated.deepcopy.go — Deep copy support for the new slice field
• pkg/controllers/monitoring/monitoring-stack/components_test.go — Unit tests for toEnableFeatures()
• test/e2e/monitoring_stack_controller_test.go — Added EnableFeatures to the managed fields e2e test

Usage

apiVersion: monitoring.rhobs/v1alpha1
kind: MonitoringStack
metadata:
  name: monitoring-stack
spec:
  prometheusConfig:
    enableRemoteWriteReceiver: true
    enableFeatures:
      - exemplar-storage

This propagates as --enable-feature=exemplar-storage on the Prometheus container args.

Motivation

We use Tempo's metrics generator to produce span-metrics (traces_spanmetrics_calls_total, traces_spanmetrics_latency_bucket) and write them to a MonitoringStack Prometheus via remote write with send_exemplars: true. The exemplars carry trace IDs enabling Metrics → Traces correlation in Grafana. Without exemplar-storage enabled on the receiving Prometheus, exemplars are silently dropped.

Currently there is no way to enable this through the MonitoringStack API. The existing enableRemoteWriteReceiver and enableOtlpHttpReceiver fields are feature-specific booleans — enableFeatures provides a generic escape hatch for any Prometheus feature flag.

[openshift-ci]

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[openshift-ci]

Hi @emilarnesen. Thanks for your PR.

I'm waiting for a rhobs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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