feat(datadog sinks): validate config at compile time

[thomasqueirozb]

Summary

Migrate the datadog_events, datadog_logs, datadog_metrics, and datadog_traces sinks to the validated config lifecycle: structural validation now runs at config-compile time and the validated state is retained for build.

References

Related: #26048

Vector configuration

NA

How did you test this PR?

• make check-clippy with sinks-datadog_events,sinks-datadog_logs,sinks-datadog_metrics,sinks-datadog_traces features
• make test with the same features, SCOPE="-E 'test(datadog)'" (119 passed)

Is this a breaking change?

• Yes
• No

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines.
• No. A maintainer will apply the no-changelog label to this PR.

Contributor Guidelines

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  • make fmt
  • make check-clippy (auto-fix with make clippy-fix)
  • make test
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[chatgpt-codex-connector]

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[thomasqueirozb]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. More of your lovely PRs please.

Reviewed commit: 93544b9a81

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• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

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