These changes aren't required for rolling out Envoy 1.26, but they were flagged in the upgrade and we should update the config before advancing the Envoy version further.
Deprecated fields we're using in MediaWiki (T402584#11121811):
[ ] envoy.config.core.v3.HeaderValueOption.append
In the API Gateway (T402584#11121920):
[ ] envoy.config.bootstrap.v3.Admin.access_log_path
[ ] envoy.config.cluster.v3.Cluster.common_http_protocol_options
[ ] envoy.config.cluster.v3.Cluster.http2_protocol_options
[ ] envoy.config.cluster.v3.Cluster.max_requests_per_connection
[ ] envoy.config.core.v3.HeaderValueOption.append
[ ] envoy.config.route.v3.HeaderMatcher.exact_match
[ ] envoy.config.route.v3.HeaderMatcher.safe_regex_match
[ ] envoy.config.route.v3.RouteAction.cors
[ ] envoy.type.matcher.v3.RegexMatcher.google_re2