udpa: filesystem list collection support for inline entries. (#13028)

This is the first PR towards filesystem support for file:/// URLs
compatible with #11264. Currently it plumbs in only LDS filesystem
support for list collections with only inline entries.

Risk level: Low (opt in)
Testing: Unit and integration tests added.

Signed-off-by: Harvey Tuch <htuch@google.com>

Mirrored from https://github.com/envoyproxy/envoy @ 108d2bcc884a0249eda26213e5dbdd0124134558

envoy/config/listener/v3/listener.proto

@@ -33,7 +33,7 @@ option (udpa.annotations.file_status).package_version_status = ACTIVE;
 // Listener list collections. Entries are *Listener* resources or references.
 // [#not-implemented-hide:]
 message ListenerCollection {
-  udpa.core.v1.CollectionEntry entries = 1;
+  repeated udpa.core.v1.CollectionEntry entries = 1;
 }
 
 // [#next-free-field: 25]

envoy/config/listener/v4alpha/listener.proto

@@ -36,7 +36,7 @@ message ListenerCollection {
   option (udpa.annotations.versioning).previous_message_type =
       "envoy.config.listener.v3.ListenerCollection";
 
-  udpa.core.v1.CollectionEntry entries = 1;
+  repeated udpa.core.v1.CollectionEntry entries = 1;
 }
 
 // [#next-free-field: 25]