(DOCSP-40367) cannot use drdl file in Atlas BIC

[JuliaMongo]

This PR adds a note that .drdl file can't be used in Atlas BI Connector. It is similar to an Atlas-side PR on the same.

DOCSP-40367

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[docs-builder-bot]

✨ Staging URL: https://preview-mongodbmongodb.gatsbyjs.io/bi-connector/master/

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• job log: 08c69e7966cc3291e15b8d0fdbbe206e3c576bfd