[DBM Doc] Add MongoDB query metrics support (Agent v7.78+)

[datadog-datadog-prod-us1]

Confidence: AUTO

Source PR: DataDog/integrations-core#23596 — "Mongo Query Metrics"

What changed

The integrations-core PR announces that MongoDB Query Metrics are now supported in Database Monitoring starting with Datadog Agent v7.78. This documentation update reflects that user-facing change in the DBM docs.

Edits

• content/en/database_monitoring/setup_mongodb/selfhosted.md
  • Added "query metrics" to the intro list of capabilities.
  • Added a note under "Before you begin": "Query metrics for MongoDB require Datadog Agent v7.78 or later."
• content/en/database_monitoring/setup_mongodb/mongodbatlas.md
  • Same two changes as above (kept in sync per DBM docs convention; DocumentDB is also covered by these MongoDB pages).
• content/en/database_monitoring/data_collected.md
  • Added MongoDB to the list of primary DBM query metric prefixes: mongodb.queries.* (with the v7.78+ requirement noted).

The individual mongodb.queries.* metrics are already present in mongo/metadata.csv, so no per-metric documentation is added.

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Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/pierreln-dd/dbm-doc-mongo-23596/database_monitoring/data_collected