Update FlightSqlService trait to pass session info along

[avantgardnerio]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

Ballista requires keeping session state for things like what tables are registered. In order to look up this state, we need a key. According to the arrow docs, this key is in the request metadata. This metadata is not passed to the impls in the existing trait, so Ballista is not able to run any query more advanced than select 1;.

Describe the solution you'd like

Agree on a format to pass session data to implements.

Describe alternatives you've considered

1. Passing raw tonic metadata
2. handling all authentication in the base impl
3. passing the 1 header info as a generic string
4. decoding it and forcing it to be a UUID
5. ...

[avantgardnerio]

CC @andygrove and @alamb

[alamb]

so Ballista is not able to run any query more advanced than select 1;

LOL