[C++] Native database interfaces

[asfimport]

Meta-task for adding native database interfaces to Arrow C++.

Reporter: Antoine Pitrou / @pitrou

Subtasks:

• [C++] Native result set adapter for PostgreSQL / libpq
• [C++] Native Arrow interface to sqlite3
• [C++] Native client interface to SQL Server / TDS protocol
• [C++] Native client interface to Clickhouse
• [C++] Native database client for MariaDB / MySQL client protocol

Related issues:

• [C++][Python][FlightRPC] Add Flight SQL ADBC driver and Python bindings (is related to)

_{Note: This issue was originally created as ARROW-11670. Please see the migration documentation for further details.}

[asfimport]

Antoine Pitrou / @pitrou:
It's not obvious to me that this should be maintained inside Arrow, rather than as third-party projects.
I can envision the build and CI consequences of having to interact with all those systems on an optional basis.

@nealrichardson thoughts?

[asfimport]

Neal Richardson / @nealrichardson:
You're probably right (though it's also probably good to track the work here)