fix: Do not try to load deleted users on app load [FS-1607]

[atomrc]

FS-1607 [web] Webapp is not removing deleted users for the `users` database

This changes the strategy we use to load the user availabilities and put them on the user enties.

What we did before was:

• load all the user availabilities in DB
• map those to locally loaded users and load missing users from the BE
  -> this would lead to querying deleted users from the server

The new strategy is:

• load all the users from backend
• for all those loaded users, find the availabilities in DB
  -> this way some availabilities might not be mapped, but that means they belonged to deleted users

[codecov]

Codecov Report

Merging #14794 (c155b49) into dev (2ae0f84) will decrease coverage by 0.02%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##              dev   #14794      +/-   ##
==========================================
- Coverage   42.82%   42.81%   -0.02%     
==========================================
  Files         621      621              
  Lines       21219    21227       +8     
  Branches     4869     4870       +1     
==========================================
  Hits         9088     9088              
- Misses      10973    10981       +8     
  Partials     1158     1158              

[przemvs]

Code LGTM :)