Support PREPARE and EXECUTE statements

[scsmithr]

Summary

Once we have the extended query protocol working, we'll want to expose the SQL level PREPARE ... and EXECUTE ... statements.

See Postgres doc: https://www.postgresql.org/docs/current/sql-prepare.html

The PR for closing out this issue should be relatively small since it'll make use of the stuff being added in for the extended query protocol.

Blocked on extended query protocol support.

Specifications

• Support PREPARE and EXECUTE in SQL queries
• SLT tests for PREPARE and EXECUTE

Rationale

Postgres compatibility.

Most clients/libraries will be using the protocol directly, but users will likely expect that we support the SQL statements too.

Impact

N/A

Tasks

See specs

[scsmithr]

apache/datafusion#4539

[greyscaled]

Stale - can reopen later