Global policy differentiation and search for 'similar' policies

### Problem description
Current implementation of policy differentiation feature further extended in #1793 allows for comparison/diff of multiple policies, but only those that 'belong' to the local instance of Guardian.

### Requirements

- Implement the ability for Guardian to compare policies produced by 'other' Guardian instances without explicitly importing them into Guardian (i.e. without it appearing in the various grids etc).
- Allow for mass-comparison of policies such that a user should be able to search for policies 'similar' to 'different' to some other policy based on some similarity threshold.

### Definition of done

- Capability exists in the Guardian
- Documentation created

### Acceptance criteria
- There is a capability in the Guardian to efficiently compare policies with a simple UX - without having to go through the import procedure.
- This architecture allows for mass-comparison of policies and identification of similarity score.

See also #1660
See also #1793