GA link exists without GA configuration

[devmount]

Describe the bug
If a subscriber hasn't configured their general availability under Schedule yet, they still can see their booking link in configuration without any hints, that they first have to set up their general availability. Accessing an unconfigured GA link always leads to a 404.

Expected behavior
It should be visible for subscribers, that they first have to set up their availability before sharing their link. Maybe with an alert on the account settings page. Up for discussion.

Screenshots

[MelissaAutumn]

We can probably have a "This schedule is not set up." error on that page. But also maybe swap the copy link button for a "Setup" that just throws them to the schedule page.

[devmount]

I think this is tightly coupled to the first login experience we discussed yesterday. Do we have a ticket for that already? I would wait with this until we have a defined first-login-user-flow.

[MelissaAutumn]

Just made one: #286