[fluent-bit] fix(fluent-bit): servicemonitor label fix

[Antvirf]

Remove release label from ServiceMonitor

Rationale

Prometheus operator is configured to scrape ServiceMonitor objects based on labels, and the common way to do this is by the release label of the Prometheus operator itself. Having a chart include its own release label in the object breaks this functionality without much added benefit.

This is already the way e.g. Grafana Alloy chart is set up.

Current behaviour

# Produces two release labels, which k8s won't accept, and helm install fails
$ helm template . --set serviceMonitor.enabled=true --set serviceMonitor.additionalLabels.release=prometheus-stack | grep -A10 "kind: ServiceMonitor"
kind: ServiceMonitor
metadata:
  name: release-name-fluent-bit-loki
  labels:
    app: fluent-bit-loki
    chart: fluent-bit-2.6.0
    release: release-name
    heritage: Helm
    release: prometheus-stack
spec:
  selector:

Behaviour after this PR

# only one `release` label - works fine
$ helm template . --set serviceMonitor.enabled=true --set serviceMonitor.additionalLabels.release=prometheus-stack | grep -A10 "kind: ServiceMonitor"
kind: ServiceMonitor
metadata:
  name: release-name-fluent-bit-loki
  labels:
    app: fluent-bit-loki
    chart: fluent-bit-2.6.0
    heritage: Helm
    release: prometheus-stack

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