docs: more detail about tracking down deprecated features (#7972)
docs: more detail about tracking down deprecated features (#7972)

Risk Level: n/a (docs only)
Testing: n/a
Docs Changes: yes
Release Notes: no
#7945

Signed-off-by: Alyssa Wilk <b9253d1ec9cc3e9d2aab68d288ba3dab3452adf6@chromium.org>

envoyproxy/envoy,lizan/envoy,lizan/envoy,lyft/envoy,eklitzke/envoy,lyft/envoy,istio/envoy,envoyproxy/envoy-wasm,jrajahalme/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy,lizan/envoy,eklitzke/envoy,lizan/envoy,jrajahalme/envoy,lyft/envoy,istio/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy,jrajahalme/envoy,lyft/envoy,istio/envoy,lizan/envoy,jrajahalme/envoy,envoyproxy/envoy-wasm,istio/envoy,envoyproxy/envoy,envoyproxy/envoy,jrajahalme/envoy,envoyproxy/envoy,lyft/envoy,envoyproxy/envoy,eklitzke/envoy,envoyproxy/envoy,envoyproxy/envoy,eklitzke/envoy,envoyproxy/envoy,jrajahalme/envoy,istio/envoy,eklitzke/envoy,eklitzke/envoy,istio/envoy,istio/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy-wasm,envoyproxy/envoy-wasm,lizan/envoy,lyft/envoy