Message about updating membership when a user can't attend an event when membership has expired

[oleast]

Is your feature request related to a problem? Please describe.
When a users tries to attend an event after their membership has expired for any reason will get the message "Dette arrangementet er kun åpent for medlemmer". This can be a bit confusing because they might not even know that their memberhsip has expired.

Describe the solution you'd like
When a users tries to attend an event with an expired membership the status_code 400 is returned from the server (this is NOT an HTTP status code, but an internal message about why they can't attend). Refactored code for it here: https://github.com/dotkom/onlineweb4/blob/2dc95f06669f2473668d6d052a057319cd0bbfe1/apps/events/constants.py#L58

It could be possible to create a good hand holding experience for the user by:

1. if the status code is 400, display a Message at the top of the page about applying for a membership with a link to the page.
2. Do an API call to check for existing memberships and see if their previous one has expired. If it has, display an alternate text with information about the expiry and link to update membership page.
3. Happy users and fewer emails about expired memberships?