[DOCS-14323/DOCS-14514/DOCS-14324] Add metrics GA processors

[maycmlee]

What does this PR do? What is the motivation?

• Adds docs for the Aggregate, Edit Tags, and Tag Cardinality Control processors.
• Adds nav items
• Adds processors to the Processor index page.

Merge readiness

• Ready for merge

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AI assistance

Additional notes

[github-actions]

Preview links (active after the build_preview check completes)

New or renamed files

• https://docs-staging.datadoghq.com/may/op-metrics-ga-processors/observability_pipelines/processors/aggregate
• https://docs-staging.datadoghq.com/may/op-metrics-ga-processors/observability_pipelines/processors/edit_tags
• https://docs-staging.datadoghq.com/may/op-metrics-ga-processors/observability_pipelines/processors/tag_cardinality_control

Modified Files

• https://docs-staging.datadoghq.com/may/op-metrics-ga-processors/observability_pipelines/processors/