net.box: add interactive transaction support in net.box

Implement `begin`, `commit` and `rollback` methods for stream object
in `net.box`, which allows to begin, commit and rollback transaction
accordingly.

Closes #5860

@TarantoolBot document
Title: add interactive transaction support in net.box
Implement `begin`, `commit` and `rollback` methods for stream object
in `net.box`, which allows to begin, commit and rollback transaction
accordingly. Now there are multiple ways to begin, commit and rollback
transaction from `net.box`: using appropriate stream methods, using 'call`
or 'eval' methods or using `execute` method with sql transaction syntax.
User can mix these methods, for example, start transaction using
`stream:begin()`, and commit transaction using `stream:call('box.commit')`
or stream:execute('COMMIT').
Simple example of using interactive transactions via iproto from net.box:
```lua
stream = conn:new_stream()
space = stream.space.test
space_not_from_stream = conn.space.test

stream:begin()
space:replace({1})
-- return previously inserted tuple, because request
-- belongs to transaction.
space:select({})
-- empty select, because select doesn't belongs to
-- transaction
space_not_from_stream:select({})
stream:call('box.commit')
-- now transaction was commited, so all requests
-- returns tuple.
```
Different examples of using streams you can find in
gh-5860-implement-streams-in-iproto.test.lua