Add ability to override the biometric prompt text client side

[vahancouver]

JIRA Ticket

SDKS-2990 - iOS - Expose Biometric Prompt to customize

Description

Add ability to override the biometric prompt text client side

During testing I discovered a bug: The prompt description was not properly set during device signing for BiometricAllowFallback type. The bug has been fixed as part of this feature.

Breakdown of changes for the feature

1. Add public member-wise initializer for Prompt
2. Add optional prompt parameter to DeviceBindingCallback.bind() method that overrides server values
3. Add optional prompt parameter to DeviceSigningCallback.sign() method that overrides server values
4. Add unit tests

Breakdown of the changes for bug fix

1. Add optional reason string to CryptoKey.getSecureKey() method, then assign it to LAContext.localizedReason property
2. Move prompt property from BiometricAuthenticator to it's parent class DefaultDeviceAuthenticator
3. Set prompt.description as reason while calling CryptoKey.getSecureKey() from DefaultDeviceAuthenticator.sign()

[spetrov]

LGTM! 👍🏻

[rodrigoareis]

Changes looks good to me