Document known limitations for Kafka Avro data format

[VineethReddy02]

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[Short summary of why you created this PR]

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Fixes #[insert issue link, if any]

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[github-actions]

Allow 10 minutes from last push for the staging site to build. If the link doesn't work, try using incognito mode instead. For internal reviewers, check web-documentation repo actions for staging build status. Link to build for this PR: http://docs-dev.timescale.com/docs-VineethReddy02-kafka-avro-limitations