As an administrator, I want to be able to limit mirror interval options in the same manner that tag expiration is done. For tag expiration, we have:

TAG_EXPIRATION_OPTIONS:

• 0s
• 1d
• 1w
• 2w
• 4w

I'd like to be able to define mirror intervals similarly, for example:

MIRROR_INTERVAL_OPTIONS:

• hour
• day
• week