MM-24135: Migrate AppError from SaveChannel/channel_store.go (#14299)

* MM-24135: Migrate AppError from SaveChannel/channel_store.go

This is the first POC of migration of store app errors to plain error.

We create a few basic error types in the store package and use
them to return the errors from store methods. In the app layer,
we inspect the error and re-create the exact app errors. This lets
us preserve the same error content, but yet move to plain errors.

Since this is a gradual migration, this means that the error inspection
code will be duplicated across the app layer whenever a store method
is invoked. But all of that should go away once we start propagating
the errors higher up the hierarchy.

There have been a significant amount of changes in the storetest and searchtest
layer, primarily because we have to rename the err variable now that it is of
a different type.

* Addressed review comments

* Made all appError origins to be CreateChannel

* Remove typed internal error

* Fix translations

* fix layer generation

Co-authored-by: mattermod <mattermod@users.noreply.github.com>

api4/scheme_test.go

@@ -424,8 +424,8 @@ func TestGetChannelsForScheme(t *testing.T) {
 		Type:        model.CHANNEL_OPEN,
 		SchemeId:    &scheme1.Id,
 	}
-	channel2, err = th.App.Srv().Store.Channel().Save(channel2, 1000000)
-	assert.Nil(t, err)
+	channel2, nErr := th.App.Srv().Store.Channel().Save(channel2, 1000000)
+	assert.Nil(t, nErr)
 
 	l4, r4 := th.SystemAdminClient.GetChannelsForScheme(scheme1.Id, 0, 100)
 	CheckNoError(t, r4)