doc: polish http/upgrades documentation (#14825)
doc: polish http/upgrades documentation (#14825)

Signed-off-by: spacewander <3c1e230d98b10a4dc9171ff1a79b1a41aca2bf47@gmail.com>
envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,lyft/envoy,envoyproxy/envoy,envoyproxy/envoy,lyft/envoy,envoyproxy/envoy,lyft/envoy,envoyproxy/envoy,lyft/envoy,envoyproxy/envoy,lyft/envoy,envoyproxy/envoy,envoyproxy/envoy,lyft/envoy,envoyproxy/envoy