fix(APIv2): bulk deletion should delete link not the entity

[skateman]

The bulk assignment was always deleting the right side from the database when unassigning. This means that when unassigning a system from a tailoring, we didn't delete the TailoringSystem record, but the System itself. Same happened for TailoringRule unassignment. Furthermore, due to the dynamic evaluation of the entities to be unassigned, the unassignment itself interfered with the assignment.

So I adjusted the unassignments to deal with the linking entities and reordered the deletion to happen before the assignment. This is something we aren't really able to test in our codebase though 😞

Secure Coding Practices Checklist GitHub Link

• https://github.com/RedHatInsights/secure-coding-checklist

Secure Coding Checklist

• Input Validation
• Output Encoding
• Authentication and Password Management
• Session Management
• Access Control
• Cryptographic Practices
• Error Handling and Logging
• Data Protection
• Communication Security
• System Configuration
• Database Security
• File Management
• Memory Management
• General Coding Practices

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.77%. Comparing base (37bc99b) to head (6b6f1e6).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2076   +/-   ##
=======================================
  Coverage   98.77%   98.77%           
=======================================
  Files         224      224           
  Lines        4722     4728    +6     
=======================================
+ Hits         4664     4670    +6     
  Misses         58       58           

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[LightOfHeaven1994]

Tested in ephemeral, works great!
Ignore CI failures as there is some issue on qe api client auth side