feat: add MongoDB datasource support (#2754)

[SaladDay]

What type of PR is this?

Feature

What this PR does / why we need it:

This PR adds MongoDB as a new datasource type to Nightingale, enabling users to query and monitor data from MongoDB databases.

Which issue(s) this PR fixes:

Fixes #2754

Special notes for your reviewer:

• the MongoDB datasource follows the same pattern as other datasources (MySQL, PostgreSQL, ClickHouse, etc.)
• connection pooling is implemented using the existing pool.PoolClient pattern
• all MongoDB-specific settings are prefixed with mongodb. for clarity;
• time range filters are automatically merged with user-provided filters when a time field is specified

[SaladDay]

@710leo ptal, thx🙏

[710leo]

@SaladDay Thank you for taking the time to work on this feature!

Before we proceed with the code review, I think it would be beneficial to have a more thorough discussion about the product design for this feature in the related issue #2871. There are a few design considerations we should clarify first:

• Does MongoDB provide an official query console we can use as a reference?
• What would a well-designed MongoDB query page look like?
• Let’s collect and review common MongoDB query use cases to ensure the proposed design meets those needs.

Once we align on the product design and user experience, it will be much easier to determine the best implementation approach. Would you mind sharing your thoughts on these questions in issue #2871? This will help us ensure the implementation meets everyone’s needs and expectations.

Looking forward to your input!