MM-24133: Migrate AppError from bot_store.go (#14339)

* 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

* MM-24132: Migrate AppError from SaveDirectChannel/channel_store.go

This PR migrates 2 new methods SaveDirectChannel and CreateDirectChannel
to return error instead of AppError.

We also need to handle the error internally in SaveMultipleMember for now
until that is migrated too.

* MM-24133: Migrate AppError from bot_store.go

* Fix errors

* Fix err

* Fix bad return

* Fix vet errors

* Fix incorrect error check

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

store/errors.go

@@ -68,6 +68,19 @@ func (e *ErrConflict) Unwrap() error {
 	return e.err
 }
 
-// TODO:
-// type ErrNotFound struct {
-// }
+// ErrNotFound indicates that a resource was not found
+type ErrNotFound struct {
+	resource string
+	Id       string
+}
+
+func NewErrNotFound(resource, id string) *ErrNotFound {
+	return &ErrNotFound{
+		resource: resource,
+		Id:       id,
+	}
+}
+
+func (e *ErrNotFound) Error() string {
+	return "resource: " + e.resource + " id: " + e.Id
+}