Add headings to appointments

[ChristophWurst]

Is your feature request related to a problem? Please describe.

From #3540

Every appointment should have a heading so it’s possible to directly navigate to it, including the time and title

Describe the solution you'd like

N/a

Describe alternatives you've considered

No response

Additional context

@jancborchardt @nimishavijay would it make sense to have a rough mockup of where this should be added and how it should look?

[jancborchardt]

I’m a bit confused about what a mockup is needed for – the heading would simply be the event title, no? And for a new event, the input with "Event title" as placeholder or label. @JuliaKirschenheuter?

[JuliaKirschenheuter]

I would say that adding invisible heading (like <h2> or <h3>) with class="hidden-visually" should be enough.