Cleanup operator instance metrics when instance is deleted

[pavolloffay]

https://issues.redhat.com/browse/TRACING-4609

Tested with

kubectl apply -f - <<EOF
apiVersion: tempo.grafana.com/v1alpha1
kind: TempoMonolithic
metadata:
  name: simplestmono
spec:
  storage:
    traces:
      backend: s3 
      size: 3Gi 
      s3: 
        secret: minio-test
EOF


kubectl apply -f - <<EOF
apiVersion: tempo.grafana.com/v1alpha1
kind: TempoStack
metadata:
  name: simplest
spec:
  storage:
    secret:
      name: minio-test
      type: s3
  storageSize: 1Gi
EOF

Then port-forward the operator 8080 and check for metric controller_runtime_reconcile_total

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 18 lines in your changes missing coverage. Please review.

Project coverage is 72.99%. Comparing base (e29848a) to head (26ef5d8).

Files	Patch %	Lines
internal/status/metrics.go	0.00%	8 Missing ⚠️
internal/webhooks/tempomonolithic_webhook.go	0.00%	5 Missing ⚠️
internal/webhooks/tempostack_webhook.go	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1019      +/-   ##
==========================================
- Coverage   73.16%   72.99%   -0.18%     
==========================================
  Files         106      106              
  Lines        6608     6624      +16     
==========================================
  Hits         4835     4835              
- Misses       1480     1496      +16     
  Partials      293      293              

Flag	Coverage Δ
unittests	72.99% <0.00%> (-0.18%)	⬇️

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[andreasgerstmayr]

lgtm 👍