[MM-27623] Add new session prop for oauth (#15221)

* Add new session prop for oauth

* Make it isOAuthUser to differentiate better

* Fix up caps

* Fix tests

* Add tests for IsOAuthUser

app/app_iface.go

@@ -461,7 +461,7 @@ type AppIface interface {
 	DoEmojisPermissionsMigration()
 	DoGuestRolesCreationMigration()
 	DoLocalRequest(rawURL string, body []byte) (*http.Response, *model.AppError)
-	DoLogin(w http.ResponseWriter, r *http.Request, user *model.User, deviceId string, isMobile, isOAuth, isSaml bool) *model.AppError
+	DoLogin(w http.ResponseWriter, r *http.Request, user *model.User, deviceId string, isMobile, isOAuthUser, isSaml bool) *model.AppError
 	DoPostAction(postId, actionId, userId, selectedOption string) (string, *model.AppError)
 	DoPostActionWithCookie(postId, actionId, userId, selectedOption string, cookie *model.PostActionCookie) (string, *model.AppError)
 	DoUploadFile(now time.Time, rawTeamId string, rawChannelId string, rawUserId string, rawFilename string, data []byte) (*model.FileInfo, *model.AppError)