Secure backup invalid state after account creation

### Steps to reproduce

Raised from #5784

It looks like sometimes we can be completely blocked with a state where the secure backup wasn't properly set, but the required secrets to set it up are not available anymore. We should probably provide a way to reset everything in that case. (but we probably need as well, to detect what actions can cause entering this specific broken state)

I only had this invalid state once, I believe the application crashed at some point which might have interrupted the backup creation process.

Will try to have more input if I ever reproduce it.

### Outcome

### Your phone model

_No response_

### Operating system version

_No response_

### Application version

_No response_

### Homeserver

_No response_

### Will you send logs?

No