feat: share prepared statements among sessions

Previously, users with multiple connections to tarantool instance
couldn't share prepared statements across sessions. They had to
manually call prepare in each session before execution.

This commit automates this process for the exported version of
SQL prepared statement execution (sql_execute_prepared_ext symbol).
Original Lua execution keeps the old behavior for backward
compatibility.

NO_DOC=picodata internal patch
NO_CHANGELOG=picodata internal patch
NO_TEST=picodata internal patch