feat(validation): add CRUD endpoints for validation bypass rules

[seansica]

This PR includes two changes, both of which are complementary to mitre-attack/attack-workbench-frontend#876

(1) Adds CRUD endpoints for validation bypass rules

• added PUT endpoint and completed controller/service/repo implementations
• wired up the routes in validation-bypasses-routes.js
• added OpenAPI tag/path/schema coverage
• added regression tests

These make it possible to manage the ADM validation bypass rules. Currently they get loaded at runtime via a server-side JSON-based config file. Now, they can be dynamically managed by clients w/o having to restart the server.

Closes #480

---

(2) Overhaul the identity service

• The backend now tracks a new key, mitre_identity_writes_enabled: bool, in the systemconfigurations collection entities.
• New GET and POST requests are added to toggle the value of the new mitre_identity_writes_enabled key: {GET,POST} /api/config/mitre-identity-writes
• The mitre_identity_writes_enabled key acts as a guard for the MITRE identity object. The REST API will block POST, UPDATE, and DELETE requests for the MITRE identity object when writes are disabled (set to false). The server will return 400 Bad Request with message Cannot create, update, or delete protected MITRE identity identity--c78cb6e5-0c4b-4611-8297-d1b8b55e40b5. Enable MITRE identity writes to modify this identity.
• New values have been added to allowed-values.json to support new form fields for identity objects. These correspond to supported values in the official identitySchema

[codecov]

Codecov Report

❌ Patch coverage is 88.30409% with 40 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.66%. Comparing base (f3fd8f1) to head (ffe610e).

Files with missing lines	Patch %	Lines
app/repository/validation-bypasses-repository.js	66.66%	12 Missing ⚠️
app/controllers/system-configuration-controller.js	62.96%	10 Missing ⚠️
...pp/services/system/system-configuration-service.js	78.37%	8 Missing ⚠️
app/controllers/validation-bypasses-controller.js	84.21%	6 Missing ⚠️
app/repository/attack-objects-repository.js	90.00%	3 Missing ⚠️
app/services/stix/identities-service.js	98.36%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             next     #481      +/-   ##
==========================================
+ Coverage   69.15%   69.66%   +0.51%     
==========================================
  Files         220      220              
  Lines       30832    31102     +270     
  Branches     2676     2765      +89     
==========================================
+ Hits        21321    21667     +346     
+ Misses       9474     9395      -79     
- Partials       37       40       +3     

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