Support multiple PostgreSQL databases at the same time

[bclermont]

What if, instead of a single DB per MCP server instance, it could be multiples.

And the name of the database could be a parameter in each tool.
At startup, all clients are initialized and store in a map[string]*sql.DB.
Have config loaded from either a file or a JSON in an environment variable

If this is something you are interested as well, I can create a PR

[habuvo]

I like the idea, it could be a great improvement for the server, thank you!