add redis cache support

[benedikt-bartscher]

https://docs.docker.com/registry/configuration/#cache
https://github.com/bitnami/charts/tree/main/bitnami/redis

storage:
  cache:
    blobdescriptor: redis
    blobdescriptorsize: 10000

redis:
  addr: localhost:6379
  password: asecret
  db: 0
  dialtimeout: 10ms
  readtimeout: 10ms
  writetimeout: 10ms
  pool:inmemory
    maxidle: 16
    maxactive: 64
    idletimeout: 300s
  tls:
    enabled: false