feat(editor): improve attendee and resource status display

[st3iny]

Resolves #4983

I refactored the logic and moved it to a computed prop to facilitate making use of the schedule status as well.

I also implemented some custom status messages if the scheduling fails for some reason (statuses 3.x and 5.x).

Screenshots

Organizer's view

Invitees	Resources

(In the example above, the user test was just added and the event was not saved yet. The same applies to the resource Croc.)

Attendee's view

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 47 lines in your changes missing coverage. Please review.

Project coverage is 23.31%. Comparing base (7ed3e6e) to head (2f8a224).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
...rc/components/Editor/AvatarParticipationStatus.vue	0.00%	38 Missing ⚠️
src/components/Editor/Resources/ResourceList.vue	0.00%	3 Missing ⚠️
src/components/Editor/Invitees/InviteesList.vue	0.00%	2 Missing ⚠️
...rc/components/Editor/Invitees/InviteesListItem.vue	0.00%	2 Missing ⚠️
...c/components/Editor/Resources/ResourceListItem.vue	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6520      +/-   ##
============================================
- Coverage     23.33%   23.31%   -0.03%     
  Complexity      453      453              
============================================
  Files           248      248              
  Lines         11777    11788      +11     
  Branches       2246     2247       +1     
============================================
  Hits           2748     2748              
- Misses         8705     8716      +11     
  Partials        324      324              

Flag	Coverage Δ
javascript	14.93% <0.00%> (-0.02%)	⬇️
php	59.29% <ø> (ø)

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