Implement GCP Secret Manager strategy

[bleuscyther]

Use Google Cloud Secret Manager to store the client_secret.

Class: Fruitsbytes\PHP\MonCash\Strategy\SecretManager\GCPSecretManager
Implements: Fruitsbytes\PHP\MonCash\Strategy\SecretManager\SecretManagerInterface

Default

# .env

MONCASH_SECRET_MANAGER="Fruitsbytes\\PHP\MonCash\\Strategy\\SecretManager\\GCPSecretManager"

Override

// cart.php

use Fruitsbytes\PHP\MonCash\Strategy\SecretManager\GCPSecretManager
  
$configuration = new Configuration(["secretManager"=> GCPSecretManager::class]);