split out from #11327
There's a bit of transitive ugliness: declaring the extensions requires security posture, requires stub build files, requires codeowners before the code move, but it'll be pretty short lived.
Risk Level: Low (mostly only APIs)
Testing: n/a
Docs Changes: some of the new docs
Release Notes: n/a
Signed-off-by: Alyssa Wilk <alyssar@chromium.org>
Mirrored from https://github.com/envoyproxy/envoy @ e8dc25ecec277c0b94d02151de79353a9ba07b4e
data-plane-api(CircleCI)