feat: mTLS support for iOS and Android

[MKmedicalvalues]

On desktop, mTLS and client certificates are handled by the browser.

On mobile however, apps (unlike the browser) are not allowed to access client certificates stored by the operating system because of security concerns. This results in apps having to handle mTLS themselves.

This change adds two optional parameters to the authenticate and refreshToken functions that allow passing pkcs data and an optional password for said data to the generic-oauth2 plugin to perform oauth2 against a server that expects client certificates.