MM-23244: Validate that AuthData and AuthService fields are mutually inclusive. (#14175)

* MM-23244: Validate that either both or neither AuthData and AuthService fields are set.

* MM-23244: Readability improvement.

* MM-23244: Adds translation. Tests for error id.

* MM-23244: Fix test.

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

app/import_functions_test.go

@@ -847,6 +847,7 @@ func TestImportImportUser(t *testing.T) {
 	require.NotNil(t, err, "Should have failed to import invalid user.")
 
 	data.AuthData = nil
+	data.AuthService = nil
 	err = th.App.importUser(&data, false)
 	require.Nil(t, err, "Should have succeeded to update valid user %v", err)