Compare EloqDoc Compatibility with FerretDB and DocumentDB

[zhangh43]

Task Description
We need to evaluate EloqDoc’s MongoDB compatibility level against other MongoDB-compatible databases — specifically FerretDB and DocumentDB. The goal is to highlight EloqDoc’s coverage, identify any missing or partially supported commands, and document compatibility differences.

Expected Outcome
A clear compatibility matrix showing where EloqDoc matches or exceeds FerretDB and DocumentDB in MongoDB API coverage, serving as the basis for marketing and technical docs.