feat: full migration to custom resource pattern

[damacus]

This PR performs a full migration of the certificate cookbook to the modern custom resource pattern.

Changes:

• Architecture: Deleted legacy attributes/ and recipes/ directories.
• Resource Modernization: Refactored the manage resource to use unified_mode true, native file resources, and proper Chef resource guards.
• New Actions: Added :delete action to the certificate_manage resource with surgically precise file removal.
• Dependency Reduction: Dropped chef-vault support to streamline the cookbook.
• Platform Updates: Modernized supported platforms across kitchen.yml and CI (Ubuntu 22.04+, Debian 12+, RHEL 8+).
• Standards: Added # frozen_string_literal: true to all Ruby files and adhered to organization rules for metadata.rb.
• Documentation: Created LIMITATIONS.md and comprehensive resource documentation in documentation/.
• Testing: Updated ChefSpec and InSpec tests; moved integration test recipes to a dedicated test cookbook; added unit tests for helper modules.

🚀 Party on! 🥳

[github-actions]

Slowest examples

Top 10 slowest examples (0.46 seconds, 61.12% of total time)

Example	Description	Time in seconds
spec/unit/resources/manage_spec.rb:143	certificate_manage with combined file is expected not to create file "/etc/pki/tls/certs/Fauxhai-bundle.crt"	0.1323
spec/unit/resources/manage_spec.rb:27	certificate_manage with default options on centos is expected to create directory "/etc/pki/tls/certs"	0.05219
spec/unit/resources/manage_spec.rb:156	certificate_manage with nginx cert is expected to create file "/etc/pki/tls/certs/fauxhai.local.pem"	0.03942
spec/unit/resources/manage_spec.rb:181	certificate_manage with action :delete is expected to delete file "/etc/pki/tls/certs/fauxhai.local.pem"	0.0374
spec/unit/resources/manage_spec.rb:89	certificate_manage with plaintext is expected to create file "/etc/pki/tls/certs/fauxhai.local.pem"	0.03559
spec/unit/resources/manage_spec.rb:53	certificate_manage with default options on ubuntu is expected to create directory "/etc/ssl/certs"	0.03506
spec/unit/resources/manage_spec.rb:136	certificate_manage with combined file is expected to create file "/etc/pki/tls/certs/fauxhai.local.pem"	0.03446
spec/unit/resources/manage_spec.rb:118	certificate_manage when not creating subdirs is expected not to create directory "/etc/pki/tls/certs"	0.0335
spec/unit/resources/manage_spec.rb:119	certificate_manage when not creating subdirs is expected not to create directory "/etc/pki/tls/private"	0.03245
spec/unit/resources/manage_spec.rb:56	certificate_manage with default options on ubuntu is expected to create file "/etc/ssl/certs/fauxhai.local.pem"	0.02828