[prometheus-blackbox-exporter] use well known label as namespace label selector

[PG2000]

What this PR does / why we need it

Kubernetes uses a well known label for namespaces. (kubernetes.io/metadata.name=)
Would be great if the network policy can match this label then.

Which issue this PR fixes

none

Special notes for your reviewer

Checklist

• DCO signed
• Chart Version bumped
• Title of the PR starts with chart name (e.g. [prometheus-couchdb-exporter])

[monotek]

i don't see why this should be the default, breaking the chart for everyone not having this label.

[PG2000]

i don't see why this should be the default, breaking the chart for everyone not having this label.

Sorry i missed to give some context.
I did this based on https://kubernetes.io/docs/reference/labels-annotations-taints/#kubernetes-io-metadata-name

[QuentinBisson]

@monotek this label is set by default on all namespaces since at least kubernetes 1.22 (c.f. https://v1-22.docs.kubernetes.io/docs/reference/labels-annotations-taints/#kubernetes-io-metadata-name)

@PG2000 I would suggest you add a kubernetes version flag so the chart uses the old way prior to 1.22 and the new way after 1.22.

Would that work for the both of you?

[monotek]

I would just make the labels generical configurable, using the old labels as default.

[PG2000]

I would just make the labels generical configurable, using the old labels as default.

I did the mentioned label selector configurable.

Just from my point of view:
The new label would makes this work out of the box for everyone with a version > 1.21

I didn't get why this should be backwards compatible for end of life k8s versions.

From my point of view:
For this you have some semantic versioning of the helm chart and more effort to maintain this with all the stuff just to be backwards compatible for end of life k8s versions.

[QuentinBisson]

@PG2000 can you bump the version?

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