refactor: text errors to text messages

[aeneasr]

Closes #428

• Refactor errors -> messages
• Write docs for messages

Additional context

BREAKING CHANGES:

Flows, request methods, form fields have had a key errors to show e.g. validation errors such as ("not an email address", "incorrect username/password", and so on. The error key is now however called messages. Each message now has a type which can be error or info, an id which can be used to translate messages, a text (which was previously errors[*].message) and This affects all login, request, settings, and recovery flows and methods.