Forbid unsupported IPROTO request types (EXECUTE, INSERT, etc.)

It is a follow-up issue from picodata#640 (closed).

Problem

Tarantool has a number of IPROTO (network protocol) request types which are handled by tarantool's internals and don't take into account picodata sql's features.

Here's an example of error which happend when using iproto execute:

Ideally we would want to redirect these requests to corresponding picodata entry points (e.g. iproto execute -> pico.sql) but it doesn't look to be worth the required effort.

Solution

Instead we should patch our tarantool fork and return errors in response to unsupported request types (basically everything except CALL).

Here's the list of request types: