VAULT-15547 First pass at agent/proxy decoupling (#20548)

* VAULT-15547 First pass at agent/proxy decoupling

* VAULT-15547 Fix some imports

* VAULT-15547 cases instead of string.Title

* VAULT-15547 changelog

* VAULT-15547 Fix some imports

* VAULT-15547 some more dependency updates

* VAULT-15547 More dependency paths

* VAULT-15547 godocs for tests

* VAULT-15547 godocs for tests

* VAULT-15547 test package updates

* VAULT-15547 test packages

* VAULT-15547 add proxy to test packages

* VAULT-15547 gitignore

* VAULT-15547 address comments

* VAULT-15547 Some typos and small fixes

command/server/config_test_helpers.go

@@ -851,6 +851,9 @@ listener "tcp" {
   agent_api {
     enable_quit = true
   }
+  proxy_api {
+    enable_quit = true
+  }
 }`))
 
 	config := Config{
@@ -891,6 +894,9 @@ listener "tcp" {
 					AgentAPI: &configutil.AgentAPI{
 						EnableQuit: true,
 					},
+					ProxyAPI: &configutil.ProxyAPI{
+						EnableQuit: true,
+					},
 					CustomResponseHeaders: DefaultCustomHeaders,
 				},
 			},