feat(datadog service): support filtering on ddtags and ddsource in datadog search syntax

[20agbekodo]

Summary

Enhance the Datadog search syntax on transforms filters: we want some keywords to query on several fields at once (OR condition):

• tags will lookup the fields tags and ddtags (previously only tags)
• source will lookup the fields source and ddsource (previously only source)
  This is because although we try to stay vendor-agnostic, the DD agent source is widely used and generates the fields ddtags and ddsource, which is misleading for Observability Pipelines users.
  Issue here (Datadog access)

Change Type

• Bug fix
• New feature (enhancement)
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

How did you test this PR?

cargo test --package vector --lib -- conditions::datadog_search::test --show-output passes all the tests.
The includes the already existing ones + what was added

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.

Checklist

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References

[bits-bot]

All committers have signed the CLA.

[pront]

Thank you @20agbekodo, nice enhancement. Tagged Vlad in case they had more thoughts but 👍 from me.

[vladimir-dd]

I think we might have to rename ddsource to source and ddtags to tags at the DD agent source, because in general DD search syntax does not recognize ddsource and ddtags.