Add ServiceAccountAnnotations override

[bt-macole]

What does this PR do?

This PR introduces [key].ServiceAccountAnnotations to the overrides for nodeAgent, clusterAgent, and clusterChecksRunner

Resolves #600

Motivation

As noted in #600, using the DD operator has some limitations with respect to easily attaching irsa role annotations to the SA.

Describe your test plan

internal/controller/datadogagent/merger/rbac and api/datadoghq/v2alpha1/ tests were updated to validate the spec update can be read and updated following the existing conventions in the dd-operator.

Note: was unable to pul the redhat base image so was unable to build--even before modifying the codebase--so was unable to run the full suite of tests or see final results in kubernetes.

Checklist

• PR has at least one valid label: bug, enhancement, refactoring, documentation, tooling, and/or dependencies
• PR has a milestone or the qa/skip-qa label

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[alai97]

Thanks for opening this PR, @bt-macole !

[bt-macole]

Thanks for opening this PR, @bt-macole !

Please let me know what else I can do to help get this feature added. It has been a bit of a pain point for my team and based on #600, for others as well. Would greatly appreciate any help to keep it moving forward.

[fanny-jiang]

Thanks for your contribution! I had just 1 small comment to update the config name to use lowercase camelcase.