Egress ACL Outer DSCP Change Table (#1743)

* Egress ACL Outer DSCP Change Table.

This document describes the High-level design of a new table type which can change the outer DSCP of a packet encapsulated by their ASIC pipeline while preserving the original packets inner DSCP value.
Feedback /Enhancements.

Investigate if we can attach the tables to the switch itself instead of the interfaces.
SAI query to see if the platform supports combining V4 and V6 tables and use a single table internally

Author: siqbal1986