feat: Add support for setting encryption configs

[mdnfiras]

Example usage in helm values:

apisix:
  encryption:
    enabled: true
    keyring:
      - "${{ENCRYPTION_KEYRING_1}}"
      - "${{ENCRYPTION_KEYRING_2}}"

extraEnvVars:
  - name: ENCRYPTION_KEYRING_1
    valueFrom:
      secretKeyRef:
        name: encryption-keyring
        key: ENCRYPTION_KEYRING_1
  - name: ENCRYPTION_KEYRING_2
    valueFrom:
      secretKeyRef:
        name: encryption-keyring
        key: ENCRYPTION_KEYRING_2