Errors are encoded as a string when serialized to MessagePack to
be sent over IProto or when just saved into a buffer via Lua
modules msgpackffi and msgpack.

That is not very useful on client-side, because most of the error
metadata is lost: code, type, trace - everything except the
message.

Next commits are going to dedicate a new MP_EXT type to error
objects so as everything could be encoded, and on client side it
would be possible to restore types.

But this is a breaking change in case some users use old
connectors when work with newer Tarantool instances. So to smooth
the upgrade there is a new session setting -
'error_marshaling_enabled'.

By default it is false. When it is true, all fibers of the given
session will serialize error objects as MP_EXT.

Co-authored-by: Vladislav <Shpilevoy&lt;v.shpilevoy@tarantool.org>

Needed for #4398