If you find yourself in a situation where you need to declare secrets for an accessory, etc. but the value of the secret is defined in your .kamal/secrets but under a different name, with the current implementation of kamal, there is no way to support this concept of aliasing/mapping.

The use case here is when you have two (or more) accessories that require the same ENV variable name, but the value is different for each accessory. For example, when defining two different Postgres backup accessories, one for your main Rails database, and another accessory for a supplementary/other database, it is not possible to have the two accessories have their own DB_PASSWORD, for example.

This PR modifies the way secrets work to support the concept of aliasing/mapping by using : as a separator. This will then allow you to declare secrets like:

accessories:
  main_db_accessory:
    env:
      secret:
        - DB_PASSWORD:MAIN_DB_PASSWORD
  secondary_db_accessory:
    env:
      secret:
        - DB_PASSWORD:SECONDARY_DB_PASSWORD

Where your .kama/secrets could look like:

SECRETS=$(kamal secrets fetch ...)
MAIN_DB_PASSWORD=$(kamal secrets extract MAIN_DB_PASSWORD $SECRETS)
SECONDARY_DB_PASSWORD=$(kamal secrets extract SECONDARY_DB_PASSWORD $SECRETS)