Refactor code structure for improved readability and maintainability

[gem-cp]

This pull request primarily adds new test certificates and configuration files for the ZETA Guard provisioning component, and updates documentation to reflect a new minor version. The changes are mostly related to test infrastructure, such as adding root and CA certificates, policy signer certificates, and federation master configuration for different environments.

Test certificates and configuration:

• Added new Apple Root CA certificate at zeta-guard-provisioning/test/apple-root-ca/apple-root.pem for use in test environments.
• Added new CA certificates: GEM.KOMP-CA61-TEST-ONLY.pem and GEM.RCA7-TEST-ONLY.pem under zeta-guard-provisioning/test/policy-engine-bundle-keys/ca/ for policy engine bundle key testing. [1] [2]
• Added a new policy signer certificate zeta-policy-freigeber-komp61.pem under zeta-guard-provisioning/test/policy-engine-bundle-keys/signers/ for use with the policy engine.
• Added a federation master configuration file zeta-guard-provisioning/test/federation-master.yaml specifying entity statement URIs for both production and test environments.

Documentation update:

• Updated the API documentation in docs/api/v1/index.md to reflect version 1.3.1-1 and the new document date.