User export

[Felix Magedanz]

In the same spirit of our existing user import feature, we need user export.

It should be in the same format / schema that we use for user import (i.e. exported Hanko data should be importable to another Hanko without any modifications):

• https://raw.githubusercontent.com/teamhanko/hanko/backend/v0.8.4/backend/json_schema/hanko.user_import.json
• https://cloud.hanko.io/examples/import_users.json

[Diptesh Choudhuri]

Hey @FlxMgdnz could you assign me this issue?