Add PostgreSQL support

[chinmayshah99]

Description

Right now, to load data into pydp, the way to use load it manually using pandas or some other method and then apply DP operations by passing it to a list.
A good way to use is to enable postgres support within DP so you don't have a scope of opening up a list.

In google's repo, they have added a postgres extesnsion. While this works in the DB, in the code, it becomes bit difficult to use.

What we could do is build support on top of the psycopg2 module, thus the SQL operations would be DP compliant.

Breakdown

What can be done is we disable Sum, Count operation from psycopg2 and define our custom functions so in no-case shall privacy be violated.

Who else?

We might need research team support for SQL queries but doesn't seem likely for statistical functions.