config: v2 transport API fatal-by-default. (#14223)

This is a followup to #13950 in which the transport API is also
fatal-by-default.

Risk level: High (this will break anyone who is still using v2 and has
not enabled CLI or runtime override)
Testing: Various tests updated as described above. New unit test added
for bootstrap to server_test and to ads_integration_test for
dynamic rejection behavior. api_version_integration_test continues to
provide the definitive cross-version transport API integration test.
Release Notes: Same as #13950.

Signed-off-by: Harvey Tuch <[email protected]>

api/envoy/api/v2/core/config_source.proto

@@ -26,10 +26,10 @@ enum ApiVersion {
   // When not specified, we assume v2, to ease migration to Envoy's stable API
   // versioning. If a client does not support v2 (e.g. due to deprecation), this
   // is an invalid value.
-  AUTO = 0;
+  AUTO = 0 [deprecated = true];
 
   // Use xDS v2 API.
-  V2 = 1;
+  V2 = 1 [deprecated = true];
 
   // Use xDS v3 API.
   V3 = 2;

api/envoy/config/core/v3/config_source.proto

@@ -27,10 +27,10 @@ enum ApiVersion {
   // When not specified, we assume v2, to ease migration to Envoy's stable API
   // versioning. If a client does not support v2 (e.g. due to deprecation), this
   // is an invalid value.
-  AUTO = 0;
+  AUTO = 0 [deprecated = true];
 
   // Use xDS v2 API.
-  V2 = 1;
+  V2 = 1 [deprecated = true];
 
   // Use xDS v3 API.
   V3 = 2;