Explore Public rooms: Batch import discover homeserver

### Your use case

Is your feature request related to a problem? Please describe.
I added a lot of discovery masters, It's too much trouble to add them manually one by one!
Batch import discover homeserver by url
For example .txt .json
https://tatsumoto-ren.github.io/matrix/#blocklist.txt
https://github.com/tatsumoto-ren/matrix/blob/main/res/blocklist.json

### Have you considered any alternatives?

_No response_

### Additional context

_No response_

### Are you willing to provide a PR?

No