feat: Add cert-manager integration with CertificateProvider interface

[adityajoshi12]

What would you like to be added?

Ability to use cert-manager for certificate issuance (related issue #212), which would:

• Eliminate the need to deploy and manage Fabric CA servers
• Enable automatic certificate renewal
• Support various issuers (ACME/Let's Encrypt, external CAs, etc.)

Proposed Solution:

Introduce CertificateProvider Interface. Refactor existing code to use an interface-based architecture:

type CertificateProvider interface {
    Enroll(ctx context.Context, req EnrollRequest) (*EnrollResponse, error)
    Reenroll(ctx context.Context, req ReenrollRequest) (*EnrollResponse, error)
    Register(ctx context.Context, req RegisterRequest) (*RegisterResponse, error)
    Revoke(ctx context.Context, req RevokeRequest) error
    GetCACertificate(ctx context.Context) (*x509.Certificate, error)
}

Implementations:

• FabricCAProvider - Wraps existing Fabric CA enrollment logic
• VaultProvider - Wraps existing Vault integration logic
• CertManager

┌─────────────────────────────────────────────────────────────┐
│                    Controllers                              │
│  (Peer Controller, Orderer Controller)                      │
└─────────────────┬───────────────────────────────────────────┘
                  │
                  │ depends on
                  ▼
┌─────────────────────────────────────────────────────────────┐
│            CertificateProvider Interface                     │
│  • Enroll(req EnrollRequest) → Certificate                  │
│  • Reenroll(req ReenrollRequest) → Certificate              │
│  • Register(req RegisterRequest) → Credentials              │
│  • Revoke(req RevokeRequest) → error                        │
└─────────────────┬───────────────────────────────────────────┘
                  │
                  │ implemented by
        ┌─────────┴─────────┬──────────────┐
        │                   │              │
        ▼                   ▼              ▼
┌──────────────┐  ┌──────────────┐  ┌──────────────┐
│  FabricCA    │  │   Vault      │  │ CertManager  │
│  Provider    │  │   Provider   │  │  Provider    │
└──────────────┘  └──────────────┘  └──────────────┘

Why is this needed?

Currently, HLF-Operator supports two ways for peers and orderers to obtain certificates:

1. FabricCA - Deploy Fabric CA server and enroll with it
2. Vault - Use HashiCorp Vault's PKI backend

Additionally, the current certificate handling code has architectural issues:

• Tight coupling between controllers and certificate providers
• Code duplication across peer and orderer controllers
• Difficult to test (requires real CA infrastructure)
• Hard to extend with new certificate providers