🐛 fix(mongodb-v2): use max 10k documents while discovering MongoDB schema

[joelluijmes]

What

Describe what the change is solving
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The mongodb v2 implementation doesn't limit the amount of documents while performing discovery. This PR remedies this behavior. The documentation of the MongoDB states the following:

Connector select 10k documents to collect all distinct field.
https://docs.airbyte.io/integrations/sources/mongodb-v2#step-1.-find-all-unique-properties

However, upon testing the integration I noticed it is taking way to long. Digging into the code I never found any references that it is limitted to 10k documents. As my source database has 1.2B documents, it makes sense why discovery taking so long 😓

Further looking around it was already mentioned on a previous PR.

the documentation probably originates from the v1 implementation, where there is an explicit limit.
https://github.com/airbytehq/airbyte/blob/5393070dc6c87c3fccad8b664cee8e30d3e52ba3/airbyte-integrations/connectors/source-mongodb/lib/mongodb_stream.rb

How

Describe the solution

This PR brings the integration in line with the behavior as described on the documentation. It does so by sampling 10k records at max. Note, the original approach used limit. I'd argue that sample is better approach for discovery.

Originally I implemented it with sample, as I thought it worked well. However, with sample of 10k documents, it is very slow. I reverted to the original limit implementation. Now it works :)

🚨 User Impact 🚨

Are there any breaking changes? What is the end result perceived by the user? If yes, please merge this PR with the 🚨🚨 emoji so changelog authors can further highlight this if needed.

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[marcosmarxm]

Thanks for the contribution @joelluijmes I requested the team to take a look and review it.

[ogirardot]

would love to see this integrated and ready to test it as I have the exact same issue

[ogirardot]

\o/