Add new GAMMA section to Gateway API Documentation #2141
Description
What would you like to be added:
A new section in Gateway API docs that explains how to get started with GAMMA, largely summarizing some of the key GEPs related to GAMMA.
Why this is needed:
We need this before the v0.8.0 release of the API when we intend to graduate GAMMA to "experimental".
/kind documentation
/area mesh
/assign @kflynn