Adding Oracle Target to the contrib package

[hsalama]

Description

Added oracledb.py to the contrib package to be used for creating oracle-based targets and tasks, in the same spirit as postgres Target.

Classes added:
OracleTarget which creates a row with INSERTED date and UPDATE_ID in a marker table. It creates the marker table if it doesn't exist
OracleQuery task which runs a query and returns OracleTarget

Motivation and Context

This was needed as I was incorporating luigi into a project that used Oracle for persistence

Have you tested this? If so, how?

I ran my jobs with this code and it works for me.

[stale]

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