Add related instances record API

Purpose: (taken from UIIN-340) Enhance the functionality in Instance record, accordion Related instances with associating Related instances by using the instance look-up component - similar to what has been implemented for e.g. Instance relationship.

Use case: (taken from UIIN-340)

1. As a cataloger I want to associate related titles to my instance record. A typical example can be, different editions, different material type; e.g. the printed version, of the audio book being cataloged, or the movie on dvd based on a printed book (the novel) etc.
2. As a cataloger I find the related instances by using the instance look up component which search within Inventory to find, e.g. the audio book version of 'The girl on the train'

Context:

Refer to UIIN-340 and UIIN-231 for how this will be used in the UI.

Work Scope:

• Introduce a new record API (similar to instance relationships) for related instances
• Properties
  • id
  • instance ID (I'm open to better names for these references, to represent that they are siblings)
  • related instance ID (I'm open to better names for these references, to represent that they are siblings)
  • relationship type (foreign key to related instances relationship type
  • All UUID properties should have standard UUID regular expression constraint (which I believe is all of them)

Design Reasoning:
During refinement, charlotte described related instances as:

• Very similar to instance relationships (hence should have similar record and API structure)
• Considered completely separate to instance relationships (hence should be a separate set of APIs)
• Has a sibling relationship rather than hierarchical one (hence the change of property names)