PIN protection functionality (alternative to Password)

[hisinbox]

Is your feature request related to a problem? Please describe. Many users will prefer digits-only fast to use PIN, instead of password

Describe the solution you'd like Add this option to secure key signup method and in the settings of secure key type accounts. and Offer to accounts, backed up with the backup phrase, to choose PIN. PIN screen should use embedded keyboard, like on iPhone unlock screen. Overall the optionality to choose PIN vs Password is very very similar to iPhone feature.

Additional context PIN protection requires account to be backed up with a backup phrase, because keyfile should be protected by Password only