Feature: Add DROP IF EXISTS for node/rel tables

[prrao87]

API

Other

Description

Based on David's comment, when using the DROP TABLE command, it can be useful to check if the table exists prior to running the statement, otherwise it may result in a Runtime error.

Seems like the DROP [IF EXISTS] statement exists in PostgreSQL, so it's intuitive enough to add to our grammar, like we did CREATE NODE TABLE IF NOT EXISTS.