Migrate Overwrite and GetMaxPostSize() in PostStore to sync by default (#10829)

* Migrate Overwrite and GetMaxPostSize() in PostStore to sync by default

* GH-10762: fix return type for mock func

* GH-10762: fix tests for MaxPostSize() mocks

* fix imports

app/post_test.go

@@ -14,7 +14,6 @@ import (
 	"github.com/stretchr/testify/require"
 
 	"github.com/mattermost/mattermost-server/model"
-	"github.com/mattermost/mattermost-server/store"
 	"github.com/mattermost/mattermost-server/store/storetest"
 )
 
@@ -565,25 +564,21 @@ func TestMaxPostSize(t *testing.T) {
 		Description         string
 		StoreMaxPostSize    int
 		ExpectedMaxPostSize int
-		ExpectedError       *model.AppError
 	}{
 		{
-			"error fetching max post size",
+			"Max post size less than model.model.POST_MESSAGE_MAX_RUNES_V1 ",
 			0,
 			model.POST_MESSAGE_MAX_RUNES_V1,
-			model.NewAppError("TestMaxPostSize", "this is an error", nil, "", http.StatusBadRequest),
 		},
 		{
 			"4000 rune limit",
 			4000,
 			4000,
-			nil,
 		},
 		{
 			"16383 rune limit",
 			16383,
 			16383,
-			nil,
 		},
 	}
 
@@ -595,12 +590,7 @@ func TestMaxPostSize(t *testing.T) {
 			mockStore := &storetest.Store{}
 			defer mockStore.AssertExpectations(t)
 
-			mockStore.PostStore.On("GetMaxPostSize").Return(
-				storetest.NewStoreChannel(store.StoreResult{
-					Data: testCase.StoreMaxPostSize,
-					Err:  testCase.ExpectedError,
-				}),
-			)
+			mockStore.PostStore.On("GetMaxPostSize").Return(testCase.StoreMaxPostSize)
 
 			app := App{
 				Srv: &Server{