[backend] Remove hardcoded opensaml dependencies

[RomuDeuxfois]

Proposed changes

• Remove hardcoded opensaml dependencies to fallback to Spring OpenSAML versions
• Refacto OpenSAML code to a separate class
• Closes this renovate -> [backend] Update opensaml.version to v5 (release/current) (major) - autoclosed #2201

[codecov]

Codecov Report

Attention: Patch coverage is 1.20482% with 82 lines in your changes missing coverage. Please review.

Project coverage is 41.38%. Comparing base (5e61c61) to head (b396818).
Report is 11 commits behind head on release/current.

Files with missing lines	Patch %	Lines
...ava/io/openbas/config/security/OpenSamlConfig.java	1.81%	54 Missing ⚠️
...va/io/openbas/config/security/SecurityService.java	0.00%	25 Missing ⚠️
...main/java/io/openbas/config/AppSecurityConfig.java	0.00%	3 Missing ⚠️

Additional details and impacted files

@@                  Coverage Diff                  @@
##             release/current    #3123      +/-   ##
=====================================================
- Coverage              41.41%   41.38%   -0.03%     
+ Complexity              2346     2342       -4     
=====================================================
  Files                    693      695       +2     
  Lines                  21291    21286       -5     
  Branches                1453     1454       +1     
=====================================================
- Hits                    8817     8809       -8     
- Misses                 11977    11980       +3     
  Partials                 497      497              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[damgouj]

Refacto and tests Ok for me, thanks !