FerretDB v2.1.0: performance improvements and key bug fixes

FerretDB has launched version 2.1.0, addressing a crucial indexing issue and enhancing its performance efficiency.

Developers using FerretDB's embeddable Go package will find that it now functions correctly, following fixes applied to the previously broken v2.0.0.

Alongside these improvements, updates were made to improve document handling in DocumentDB and console logging with colorized levels.

Finally, FerretDB now seamlessly integrates with Docker Secrets by allowing the PostgreSQL connection URL to be read from a file using the --postgresql-url-file flag or the FERRETDB_POSTGRESQL_URL_FILE environment variable.