docs(proposal): Gateway API annotation placement clarity proposal

Addresses kubernetes-sigs#5901
Related: kubernetes-sigs#4056

Propose comprehensive solutions for Gateway API annotation placement confusion,
including both short-term documentation improvements and long-term annotation
inheritance strategy.

Documentation improvements are proposed separately in PR kubernetes-sigs#5918 for quick merge.

Co-Authored-By: Claude <[email protected]>

Author: lexfrei