protoxform: Add enum deprecation support. (#11199)

Support deprecating an enum stanza as a whole by "option deprecated = true;"

Risk Level: low
Testing: Added test case; manually verified the generated config removes the deprecated enum
Docs Changes: N/A
Release Notes: N/A

Signed-off-by: pengg <pengg@google.com>

Mirrored from https://github.com/envoyproxy/envoy @ dbb67aa4968e7ecffaff25c1723675de569b5c59

envoy/config/route/v3/route_components.proto

@@ -552,6 +552,8 @@ message RouteAction {
   // Configures :ref:`internal redirect <arch_overview_internal_redirects>` behavior.
   // [#next-major-version: remove this definition - it's defined in the InternalRedirectPolicy message.]
   enum InternalRedirectAction {
+    option deprecated = true;
+
     PASS_THROUGH_INTERNAL_REDIRECT = 0;
     HANDLE_INTERNAL_REDIRECT = 1;
   }

envoy/config/route/v4alpha/route_components.proto

@@ -552,13 +552,6 @@ message RouteAction {
     NOT_FOUND = 1;
   }
 
-  // Configures :ref:`internal redirect <arch_overview_internal_redirects>` behavior.
-  // [#next-major-version: remove this definition - it's defined in the InternalRedirectPolicy message.]
-  enum InternalRedirectAction {
-    PASS_THROUGH_INTERNAL_REDIRECT = 0;
-    HANDLE_INTERNAL_REDIRECT = 1;
-  }
-
   // The router is capable of shadowing traffic from one cluster to another. The current
   // implementation is "fire and forget," meaning Envoy will not wait for the shadow cluster to
   // respond before returning the response from the primary cluster. All normal statistics are