feat: suppot to_char sql function

- update sbroad submodule to commit with support of to_char
- add some integration tests, note: there are also
integration tests in cartridge
- This function is implemented as calling `format` on
given datetime object
- Usage:

to_char(datetime, format)

select to_char(datetime_column, 'Last updated: %Y-%m-%d') from t

Second argument is optional and could be specified as `null`:

select to_char(datetime_column, null) from t

- format is specified with the same rules as in strftime function
https://man.freebsd.org/cgi/man.cgi?query=strftime&sektion=3