fix(opentelemetry-operator): remove default resource values

[Starefossen]

Having default values makes it impossible to remove the CPU limits since the default values will always be merged in with anything set by the user. Setting CPU limits are considered an anti pattern ref. https://komodor.com/learn/kubernetes-cpu-limits-throttling/

[TylerHelmuth]

@Starefossen if you're not using this chart as a subchart you can do:

resources:
  limits:
    cpu: null
    memory: 512Mi

But we can follow the same pattern/reasoning as #745

[github-actions]

This PR was marked stale due to lack of activity. It will be closed in 14 days.

[TylerHelmuth]

@Starefossen please include an entry in UPGRADING.md like https://github.com/open-telemetry/opentelemetry-helm-charts/blob/main/charts/opentelemetry-collector/UPGRADING.md#0531-to-0540

[Starefossen]

@Starefossen please include an entry in UPGRADING.md like main/charts/opentelemetry-collector/UPGRADING.md#0531-to-0540

Done

[TylerHelmuth]

@Starefossen lets also add a warning in NOTES.txt like the collector chart:

opentelemetry-helm-charts/charts/opentelemetry-collector/templates/NOTES.txt

Lines 39 to 41 in 50fb31f

	{{- if not .Values.resources }}
	[WARNING] No resource limits or requests were set. Consider setter resource requests and limits for your collector(s) via the `resources` field.
	{{ end }}