Custom fields / user data

It could be beneficial if Hanko would allow storing additional user data. This could make another user table unnecessary for certain use cases and thus speed up app development with Hanko even more.

First ideas for custom fields that came up were:

• Name (e.g. for email personalization)
• Marketing consent
• Phone number
• Foreign IDs (e.g. Stripe)
• Age
• Address

Setting this up per Hanko instance would require some form of definition of supported data fields and ways to add the desired fields to the config. The Hanko backend data model would have to be upgraded accordingly to be able to handle this "dynamic" data per user.

Additionally, but not necessarily, it may be desired to show or even require some or all of those fields during onboarding in hanko-auth and allow editing in hanko-profile which means that properties like labels, placeholder texts, and maybe even input validation need to be taken into consideration as well.