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>

store/timer_layer.go

@@ -1553,7 +1553,7 @@ func (s *TimerLayerChannelStore) Restore(channelId string, time int64) *model.Ap
 	return resultVar0
 }
 
-func (s *TimerLayerChannelStore) Save(channel *model.Channel, maxChannelsPerTeam int64) (*model.Channel, *model.AppError) {
+func (s *TimerLayerChannelStore) Save(channel *model.Channel, maxChannelsPerTeam int64) (*model.Channel, error) {
 	start := timemodule.Now()
 
 	resultVar0, resultVar1 := s.ChannelStore.Save(channel, maxChannelsPerTeam)