* 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>
729a84a3e6