Dynamic collection references based on attribute value

[paynejd]

Ability to define a collection by an attribute or custom attribute value (e.g., create a collection of all MER Indicator concepts with the custom attribute "Indicator Type" = "Result). The dynamic references should be resolved to actual resources and frozen when a repo version is created. There are many other types of dynamic references that are possible, and this covers a single type.

[jamlung-ri]

This ticket was already developed and should be available with the #181 work