Configure merge behavior in Hiera data

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Hiera uses a key’s configured merge behavior in any lookup that doesn’t explicitly override it.

In any Hiera data source, including module data:

Use the lookup_options key to configure merge behavior.

For example:

# <ENVIRONMENT>/data/common.yaml
lookup_options:
  ntp::servers:     # Name of key
    merge: unique   # Merge behavior as a string
  "^profile::(.*)::users$": # Regexp: `$users` parameter of any profile class
    merge:          # Merge behavior as a hash
      strategy: deep
      merge_hash_arrays: true

Hiera uses the configured merge behaviors for these keys.

Note: The hiera_* functions always override configured merge behavior.