Change console prefix when waiting for delimiter in connect/admin cli

In connect cli if no delimiter was found, when enter is pressed the input simply continues on the next line with the same picodata> prefix. So a user might think that they submitted a request while in reality they have not.

Let's fix this by indicating when we are still waiting for input with a different prefix:

picodata> select *
        > from
        > _pico_user;
...
(6 rows)
picodata>

tarantool cli has similar behavior to the one suggested.