Fetch certificate validation context using SDS service. (#4355)
Fetch certificate validation context using SDS service. (#4355)

 Refactor SdsApi to support dynamic certificate validation context, and support Envoy to fetch certificate validation context from remote server via SDS API.
Risk Level: Low
Testing: Unit tests and integration tests.
Fixes #1194

Signed-off-by: JimmyCYJ <jimmychen.0102@gmail.com>

Mirrored from https://github.com/envoyproxy/envoy @ 15cfc5ad1a4d622126f642fa70699af753a2d310

lyft/envoy-api,lyft/envoy-api,lyft/envoy-api