Add member_of_orgs as JSONB to organizations

[roaldchristesen]

Add an optional member_of_orgs field to the organization table to represent the organizations in which an organization has a membership or other formal relationship.

The field should use jsonb and contain an array of objects with an organization UUID and a role.

Example:

[
  {
    "uuid": "019d35a0-3cd1-7c28-b3ca-537e8577defe",
    "role": "member"
  },
  {
    "uuid": "019d35a0-3cd1-7c28-b3ca-537e8577def0",
    "role": "partner"
  }
]

Supported roles should initially include:

• member
• sponsor
• partner
• media_partner
• funding_partner
• cooperation_partner
• cultural_partner

The list should remain extensible so additional relationship roles can be added later.

Requirements

• Add an optional member_of_orgs jsonb field to the organization table/model.
• The field may be NULL when no such relationships exist.
• Each entry must contain:
  • uuid — UUID of the related organization.
  • role — type of relationship.
• Store UUIDs as JSON strings.
• Support querying organizations by related organization UUID and optionally by role.
• Add an appropriate JSONB GIN index if these relationships are expected to be queried frequently.
• Update the API and data model documentation accordingly.