Upgrade grpc-gateway dependency (#3257)

* proto: correct classification of authz token

The target authorization token had the invalid classification
"private". Fortunately, classification is a fail-closed system,
so this won't have exposed users authorization tokens, but
we should still use the correct classification. Use "secret".

* scripts: add Go script to remove gotags comments

The new version of grpc-gateway includes our gotags
comments in the generate swagger documentation. This
script removes all mentions of these.

* Upgrade grpc-gateway dependency

Mainly we need this to fix generation of our docs side API docs,
but it also includes a nice fix for the new Download RPC, i.e. it
now contains the correct response schema (a binary stream).

internal/proto/controller/api/resources/targets/v1/target.proto

@@ -372,7 +372,7 @@ message SessionAuthorization {
   string type = 80; // @gotags: `class:"public"`
 
   // Output only. The marshaled SessionAuthorizationData message containing all information that the proxy needs.
-  string authorization_token = 90 [json_name = "authorization_token"]; // @gotags: `class:"private"`
+  string authorization_token = 90 [json_name = "authorization_token"]; // @gotags: `class:"secret"`
 
   // Output only. The endpoint address that the worker will connect to, useful for setting TLS parameters.
   string endpoint = 100; // @gotags: `class:"public"`