🐛 Fixed incorrect member subscription details in Admin

[allouis]

fixes https://linear.app/tryghost/issue/ENG-642

• When a subscription is in the canceled state the corresponding Member has no access to the Ghost site. The only time a Member will continue to have access if their subscription is due to cancel at the period end is if it is still in an active state, which is one of active trialing unpaid or past_due
• When a subscription is canceled immediately (i.e. before the end of the current billing period), we now render "Ended" without a date, because we don't store the cancellation date in the subscription object. We previously used "Ended {current_period_end}" which would sometimes lead to dates in the future
• Bonus: refactored code and added unit tests

[allouis]

@ronaldlangeveld This might be useful - I haven't tested this, and ideally we would use different properties here, e.g. hasAccess and switch on that instead - but I believe the fix is along these lines.