Review all validation models and make sure we don't require something we don't use.

[steinmn]

Follow-up to #351, #354 and #357

Also check if there is anything we currently don't require in validation that should be added because the lack of it would cause other issues.

Make sure to run a test with a User-role-only test-user before merging anything. We may also want to consider distinguishing between FullInstallation (returned if owner role) and LimitedInstallation (returned if only user role), since the Installations list will include all installations the user has access to, even if they do not use it in our integration (because they only have the user role for it).

[sveinse]

It seems we're not out of the woods in #357 (comment) . In this example its IsOnline which is a parameter directly used in an entity. According to the API docs: https://docs.zaptec.com/reference/api_chargers_get, IsOnline is boolean (no null). So how can we really make any assumption about the pretense of any entries?