sys/config: config state endpoint (#7424)

* sys/config: initial work on adding config state endpoint

* server/config: add tests, fix Sanitized method

* thread config through NewTestCluster's config to avoid panic on dev modes

* properly guard endpoint against request forwarding

* add http tests, guard against panics on nil RawConfig

* ensure non-nil rawConfig on NewTestCluster cores

* update non-forwarding logic

* fix imports; use no-forward handler

* add missing config test fixture; update gitignore

* return sanitized config as a map

* fix test, use deep.Equal to check for equality

* fix http test

* minor comment fix

* config: change Sanitized to return snake-cased keys, update tests

* core: hold rlock when reading config; add docstring

* update docstring

http/forwarding_test.go

@@ -582,3 +582,24 @@ func TestHTTP_Forwarding_HelpOperation(t *testing.T) {
 	testHelp(cores[0].Client)
 	testHelp(cores[1].Client)
 }
+
+func TestHTTP_Forwarding_LocalOnly(t *testing.T) {
+	cluster := vault.NewTestCluster(t, nil, &vault.TestClusterOptions{
+		HandlerFunc: Handler,
+	})
+	cluster.Start()
+	defer cluster.Cleanup()
+	cores := cluster.Cores
+
+	vault.TestWaitActive(t, cores[0].Core)
+
+	testLocalOnly := func(client *api.Client) {
+		_, err := client.Logical().Read("sys/config/state/sanitized")
+		if err == nil {
+			t.Fatal("expected error")
+		}
+	}
+
+	testLocalOnly(cores[1].Client)
+	testLocalOnly(cores[2].Client)
+}