MM-12849 Moving all non request scoped items to Server struct (#9806)

* Moving goroutine pool

* Auto refactor

* Moving plugins.

* Auto refactor

* Moving fields to server

* Auto refactor

* Removing siteurl duplication.

* Moving reset of app fields

* Auto refactor

* Formatting

* Moving niling of Server to after last use

* Fixing unit tests.

app/post_test.go

@@ -648,9 +648,9 @@ func TestMaxPostSize(t *testing.T) {
 
 			app := App{
 				Srv: &Server{
-					Store: mockStore,
+					Store:  mockStore,
+					config: atomic.Value{},
 				},
-				config: atomic.Value{},
 			}
 
 			assert.Equal(t, testCase.ExpectedMaxPostSize, app.MaxPostSize())