Store FTUE use case in an account setting

### Your use case

#### What would you like to do?

Migrate the FTUE use case value from the local device to an account setting with the key `FTUE.useCaseSelection`

#### Why would you like to do it?

Web is now tracking that data in the account setting. See the implementation https://github.com/matrix-org/matrix-react-sdk/pull/8984

#### How would you like to achieve it?

iOS is asking the use case question to user and storing that information on device. I would like to change the logic to that in the future all answers to this question are set in the account setting `FTUE.useCaseSelection`.

If the account that the user is logging into has already a value set, the FTUE use case selection screen should be skipped entirely.

Finally we should add a snippet of code that migrates the existing "on device use case selection" to the account setting.

### Have you considered any alternatives?

_No response_

### Additional context

_No response_