[FEATURE] New field type Unique

[trueromanus]

Is your feature request related to a problem? Please describe.
In some cases need to get access from postscript to single query. But how to address different query, query don't have any unique (or containing unique identifier) fields.

Describe the solution you'd like
A new field type unique needs to be added to specify these unique identifiers. If there is more than one query with the same value in unique field, a warning will be displayed. The warning will contain information about the behavior in this case. The behavior will be to get the first request with the sought unique identifier, the order is not guaranteed.