Update yaml code blocks for custom resource collection

[JacksonDavenport]

What does this PR do? What is the motivation?

Add yaml syntax highlighting to the code blocks and update the Helm / Operator configs to include a bit more of the surrounding config context.

As for example didn't want a customer setting that at the wrong root level like so:

datadog:
  apiKeyExistingSecret: datadog-agent
  #(...)
orchestratorExplorer:
  customResources:
    - <CUSTOM_RESOURCE_NAME>

Merge instructions

Merge readiness:

• Ready for merge

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Additional notes

[github-actions]

Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/jack.davenport/custom-resource-code-blocks/infrastructure/containers/configuration