Adding podcast by RSS feed option absent now/缺少按RSS添加播客功能

### Checklist - [x] I have used the search function for [**OPEN**](https://github.com/XilinJia/Podcini/issues) issues to see if someone else has already submitted the same bug report. - [x] I have **also** used the search function for [**CLOSED**](https://github.com/XilinJia/podcini/issues?q=is%3Aissue+is%3Aclosed) issues to see if the problem is already solved and just waiting to be released. - [x] I will describe the problem with as much detail as possible. - [x] If the bug only to occurs with a certain podcast, I will include the URL of that podcast. ### App version 8.18.0 ### Where did you get the app from Google Play ### Android version HarmonyOS 5.1.0 (HarmonyOS NEXT, Android compatible mode) ### Device model _No response_ ### First occurred _No response_ ### Steps to reproduce _No response_ ### Expected behaviour _No response_ ### Current behaviour there is no "Adding podcast by RSS feed" option in adding podcast screen. 添加播客界面中缺少“按RSS添加播客”选项。 ### Logs _No response_