Specific DSN settings for FlightSQL clients

Paul, [via Slack ](https://influxdata.slack.com/archives/CDBJ35NBV/p1678461872443299)

> Our own cloud documentation should include the information for what specific DSN settings FlightSQL clients should have.

From the thread:

The README https://github.com/srebhan/arrow/tree/driver/go/arrow/flight/flightsql/driver#influxdata-iox has a section for "connecting to IOx". FlightSQL doesn't include a spec for pointing to a given database or bucket or schema or namespace or whatever the underlying database uses as it's unit of organization.
So the DSN must include a parameter to specify which bucket we're querying. That's also in the slack thread linked above.
That syntax is only for cloud MT. In cloud CST, we should move to namespace as that's what we'll be using in v3.

The current Cloud2 FlightSQL implementation already supports token (which resolves the org) and bucket-name. However IIRC this ain't backed directly by IOx but queryrouterd.
Now if we look directly at IOx this depends on the method:
do_get uses an "opaque" ticket (which is protobuf), that contains the SQL text and namespace
to get a ticket you call get_flight_info . That one indeed accepts a gRPC "header" (sometimes also called metadata) called iox-namespace-name
That's not standard though which is a bit sad (the headers are "application-defined"). There's upstream discussion though if that should be added to the FlightSQL standard in a more streamlined way, see https://lists.apache.org/thread/fd6r1n7vt91sg2c7fr35wcrsqz6x4645

##### Relevant URLs
- _Provide relevant URLs (issues, community threads, existing doc pages, etc.)_

Start with the linked Arrow FlightSQL README section on connecting to IOx and review the Slack context referenced in the issue. Document the correct DSN settings for Cloud MT and Cloud CST, including bucket or namespace selection, and verify that the guidance matches the current client behavior.

Written by the indexing model from the issue text.