Use mouse click to add a new time slot

[renefs]

This issue resolves #490 .

1. When the timeline is clicked, a new slot with the default duration is added.
2. A tooltip is displayed on mouse hover to indicate the position in the timeline.
3. The granularity is set to 15 minutes, but it can be changed using the time picker.

Screen.Recording.2024-10-22.at.09.28.58.mov

[tomasr8]

Overall looks good! I just have some points regarding UX:

• Could we reuse the existing tooltip when hovering over the timeline? There are now two different tooltips which might look a bit off
  

• The green area looks a bit different now, was that intentional?
  before:
  
  after:
  
  Related to that, it's also more difficult to create parallel timeslots because of the reduced padding (there's only a tiny spot at the bottom where you can click):
  

• Maybe we could use cursor: pointer to make it more obvious that you can click on the timeline?

• The tooltip renders when you hover the + button:
  

As I mentioned here, maybe we could render a silhouette when simply hovering to make it even more obvious you're supposed to click on the timeline?