Make "Custom AWF Configuration" and " Custom MCP Gateway Configuration" internal-only, remove from docs

[dsyme]

We want to make "Custom AWF Configuration" internal only, remove from docs.

https://github.github.com/gh-aw/reference/sandbox/#custom-awf-configuration

Likewise "Custom MCP Gateway Configuration"

https://github.github.com/gh-aw/reference/sandbox/#configuration-options

These are now implementation/debugging details.