Migrate Get/GetFromMaster methods from ChannelStore to return error interface (#14688)

* Advances

* Migration finished

* Rename err to normalized error

* fix imports

* Renamed key

* Renamed key

* Suggestions

* Fix i18n

* Fix tests

Co-authored-by: Jesús Espino <jespinog@gmail.com>
Co-authored-by: Agniva De Sarker <agnivade@yahoo.co.in>

api4/group_test.go

@@ -714,7 +714,7 @@ func TestGetGroupsByChannel(t *testing.T) {
 		require.True(t, *groups[0].SchemeAdmin)
 
 		groups, _, response = client.GetGroupsByChannel(model.NewId(), opts)
-		assert.Equal(t, "store.sql_channel.get.existing.app_error", response.Error.Id)
+		assert.Equal(t, "app.channel.get.existing.app_error", response.Error.Id)
 		assert.Empty(t, groups)
 	})
 }