Non existing member attributes in settings

[epipav]

We have some attributes in some members that are non existing in member attribute settings.
This is probably happened after migrating data to dynamic attributes.

• Now instead of throwing a 400 error, we're deleting the non-existing attribute from the payload before upserting the member. This will also enable us to clear up the already existing member attributes data.
• Also fixes the wrong calculation of seconds until end of month when it's the last day of the month.

Checklist ✅

• Label appropriately with Feature, Enhancement, or Bug.
• Tests are passing.
• New backend functionality has been unit-tested.
• Environment variables have been updated:
  • Local frontend configuration: frontend/.env.dist.local, frontend/.env.dist.composed.
  • Local backend: backend/.env.dist.local, backend/.env.dist.composed.
  • Configuration docs have been updated.
  • Team members only: update environment variables in override, staging and production env. files and trigger update config script.
• API documentation has been updated (if necessary) (see docs on API documentation).
• Quality standards are met.
• All changes have been tested in a staging site.
• All changes are working locally running crowd.dev's Docker local environment.