Remove Metrics Server APIService in finalizer

[carloscastrojumo]

What does this PR do?

Call cleanupMetricsServerAPIService function in datadogagent finalizer.

Motivation

Starting in Kubernetes 1.20 version, when deleting the datadogagent resource, or delete the datadog namespace, the metrics service APIService is not removed, leading to a stuck namespace state at Terminating.

NAME                                   SERVICE                                        AVAILABLE                 AGE
v1beta1.external.metrics.k8s.io        datadog/datadog-cluster-agent-metrics-server   False (ServiceNotFound)   2m15s

I did not found this scenario in Kubernetes version <= 1.19.

Additional Notes

I'm not sure if I'm calling the cleanupMetricsServerAPIService in the best spot. Open for feedback.

Describe your test plan

You can test this issue by creating a testing cluster (eg: using kind) with Kubernetes version >= 1.20 and deploy the Datadog Operator. Remove the datadogagent resource or delete the datadog namespace and check if the apiservice is removed.

Repeat the same step but deploying Datadog Operator with this fix, the APIService will be removed upon deleting datadogagent resource.

[github-actions]

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[codecov-commenter]

Codecov Report

Merging #333 (078748f) into main (5a31233) will decrease coverage by 0.02%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main     #333      +/-   ##
==========================================
- Coverage   63.21%   63.18%   -0.03%     
==========================================
  Files          60       60              
  Lines        6606     6609       +3     
==========================================
  Hits         4176     4176              
- Misses       2126     2129       +3     
  Partials      304      304              

Flag	Coverage Δ
unittests	63.18% <0.00%> (-0.03%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
controllers/datadogagent/finalizer.go	30.76% <0.00%> (-4.02%)	⬇️

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