feat: Add --skip-decrypt option to bypass decryption

### Problem Statement In CI/CD or Coding Agent environments, secret keys (GPG, KMS, etc.) are often unavailable. Currently, helm-secrets always attempts decryption, blocking chart validation in keyless environments. Additionally, there are cases where you intentionally don't want CI/CD pipelines or Coding Agents to access decrypted secrets for security reasons. ### Proposed Solution Add --skip-decrypt option and HELM_SECRETS_SKIP_DECRYPT environment variable to pass encrypted files/values as-is. ``` helm secrets --skip-decrypt template ./chart -f secrets.yaml HELM_SECRETS_SKIP_DECRYPT=true helm secrets decrypt secrets.yaml ``` ### Environment - Helm Version: - Helm Secrets Version: - OS: - Shell: ### Additional information _No response_ ### Acceptance Criteria - [ ] --skip-decrypt CLI option - [ ] HELM_SECRETS_SKIP_DECRYPT environment variable - [ ] Works with -f/--values, --set, and decrypt command - [ ] Documentation added