[backend] fix backgroundTask filter issue

[yassine-ouaamou]

Proposed changes

• Mapping properly the filterMode (AND/OR)

Related issues

• Background task for negative filter is not correctly computed #4071

Checklist

• I consider the submitted work as finished
• I tested the code for its functionality
• I wrote test cases for the relevant uses case
• I added/update the relevant documentation (either on github or on notion)
• Where necessary I refactored code to improve the overall quality

Further comments

To test this fix, you need to create a background task of deletion using a negative filter on Technical

• Create a user "A"
• Import a bunch of entites as "A"
• Go to "Data" > "Entities"
• Apply a filter on "Technical creator" in a way to exclude all the users except the entites of the user "A"
• Select all the entites and delete them
• The number shown on the top of the list (or in the background task popup must be the same as the number of entites in the background task screen
  Here are screeshots from the issue where you see different numbers:
  

[SarahBocognano]

Tested ✅ Works Fine