fix(falcosidekick): Allow overriding the Prometheus scrape Service annotation

[TiagoJMartins]

What type of PR is this?

/kind bug
/kind chart-release

Any specific area of the project related to this PR?

/area falcosidekick-chart

What this PR does / why we need it:

We are working on a migration from a deprecated Prometheus setup to one based on the Prometheus Kubernetes Operator.
Since metrics scraped by the operator-managed instances are targeting ServiceMonitor and PodMonitor resources, we need to be able to configure the prometheus.io/scrape Service annotation to gradually disable scraping from our deprecated instances.

Which issue(s) this PR fixes:

Because the prometheus.io/scrape annotation is hard-coded in the Service template and it's the last entry in the annotations map, there's no way to include custom values after it.

This PR simply moves the hard-coded annotation to before the user-provided values, so at least they have an escape hatch in case they need to override the value.

Special notes for your reviewer:

You can test with:

helm template falcosidekick charts/falcosidekick -s templates/service.yaml -f - <<EOF | yq '.metadata.annotations["prometheus.io/scrape"]'
service:
  annotations:
    prometheus.io/scrape: "false"
EOF

The final template will include duplicate values, but the override will take precedence when the yaml gets parsed/applied to the cluster.

apiVersion: v1
kind: Service
metadata:
  name: falcosidekick
  annotations:
    prometheus.io/scrape: "true"
    prometheus.io/scrape: "false"
  ...

The duplicated keys will be removed by the cluster.

I considered going with a different approach based on something like .Values.service.prometheusScrape, but decided against it due to it requiring changes to the values.yaml structure.

Checklist

• Chart Version bumped
• CHANGELOG.md updated

[poiana]

Welcome @TiagoJMartins! It looks like this is your first PR to falcosecurity/charts 🎉

[poiana]

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[rsicart]

And what about removing the hard-coded annotation and putting it by default in .Values.service.annotations?