Add Read-Only Mode in Vault Settings

### Please agree to the following

- [X] I have searched [existing issues](https://github.com/cryptomator/ios/issues?q=) for duplicates
- [X] I agree to follow this project's [Code of Conduct](https://github.com/cryptomator/ios/blob/develop/.github/CODE_OF_CONDUCT.md)

### Summary

Add read-only mode option in the vault settings.

### Motivation

Users who frequently access encrypted vaults may encounter situations where they need to ensure the integrity of their encrypted files without the risk of accidental modifications or deletions. By introducing a read-only mode unlock option, users can access their vaults while preventing unintended alterations to their encrypted data.

A user mentioned as an example that they fill a vault automatically via the Desktop app. The vault is basically used as an archive. In that case, it would make sense to access this particular vault in read-only mode.

### Considered Alternatives

_No response_

### Anything else?

The Desktop app already has a read-only mode option in the vault options (if the virtual drive technology supports it). This shouldn't be too hard to implement, since we already have a read-only mode option in the free version.