docs: clean up the protocol docs and make it consistent (#42713)

## Description

This PR cleans up the protocol docs and makes it consistent to rest of
the codebase.

---

**Commit Message:** docs: clean up the protocol docs and make it
consistent
**Additional Description:** Cleans up the protocol docs and makes it
consistent to rest of the codebase.
**Risk Level:** N/A
**Testing:** CI
**Docs Changes:** N/A
**Release Notes:** N/A

Signed-off-by: Rohit Agrawal <[email protected]>

Mirrored from https://github.com/envoyproxy/envoy @ f7b8136ffb2a1014f23473ff8b4d701b86bc5e41

Author: update-envoy[bot]