Remove dependency on pre-installed Postgres libraries

[aaronsteers]

Apologies if this question has already been asked and answered, but would it be possible to remove the requirement for pre-installed Postgres? Either by refactoring around the dependency on singer-target-postgres or by using a fork that uses psycopg2-binary in place of psycopg2?

It can sometimes be confusing or time consuming for new users to have to install the Postgres dependency ahead of landing data in Snowflake.

Happy to contribute cycles if we can help in any way. Thanks!

Regarding this error message during install:

    Error: pg_config executable not found.
    
    pg_config is required to build psycopg2 from source.  Please add the directory
    containing pg_config to the $PATH or specify the full executable path with the
    option:
    
        python setup.py build_ext --pg-config /path/to/pg_config build ...
    
    or with the pg_config option in 'setup.cfg'.
    
    If you prefer to avoid building psycopg2 from source, please install the PyPI
    'psycopg2-binary' package instead.
    
    For further information please check the 'doc/src/install.rst' file (also at
    <https://www.psycopg.org/docs/install.html>).