Enhance VCkit API Documentation for Database Encryption Key Configuration

[ashleythedeveloper]

As a VCkit maintainer,
I want to add information about database encryption key configuration to the VCkit API documentation,
So that implementers can properly understand and configure the database encryption key for the VCkit API server.

Acceptance Criteria:

• Add a new section in the API server installation documentation specifically about database encryption keys
• Document the purpose of the dbEncryptionKey configuration
• Include details about the key type (X25519)
• Add instructions for generating a new encryption key using the veramo config gen-key command
• Include example configuration showing proper key usage in agent.yml
• Add warning about not using the example key in production environments
• Review and validate documentation accuracy with the core maintainers