support storing `links` info at interface level

[zebapy]

moving from code comment https://github.com/faradayio/sdk_docs/pull/25/files#r870373284

To support managing https://swagger.io/docs/specification/links/ sanely, we should add a feature to openapi-interfaces that will allow us to store the link resolution info at the content definition type (interface?) and populate it at any paths that given interface is resolved

interfaces:
    Scope:
      $includes: "Resource"
      description: Instructions on how to produce output data.
      members:
        resource_type:
          schema:
            example: scopes
        id:
          schema:
            example: 8e63467d-9478-4fba-b05a-d5e98fd06d12
        preview:
          required: false
          mutable: true
          schema:
            type: boolean
            example: true
            description: |
              A preview scope provides only a limited number of output records, but
              it is not billed.
        population:
          required: true
          initializable: true
          mutable: true
          schema:
            $interface: "ScopePopulation#SameAsInterface"
        payload:
          required: true
          initializable: true
          schema:
            $interface: "ScopePayload#SameAsInterface"
      # We would love to be able to do this but we need to figure out the details
      # links:
      #   population_cohorts:
      #     operationId: getScopePopulationCohorts
      #     parameters:
      #       scope_id: "#/id"

We should then auto populate the links info anywhere a Scope is resolved

  /scopes/{scope_id}:
    get:
      tags:
        - scopes
      summary: Retrieve a scope
      description: Get details on a specific scope
      operationId: getScope
      parameters:
        - name: scope_id
          in: path
          description: The UUID of a scope
          required: true
          schema:
            type: string
            format: uuid
      responses:
        200:
          description: Information about the scope
          content:
            application/json:
              schema:
                $interface: "Scope"
          links: # openapi-interfaces should set links here
            populationCohorts:
              operationId: getScopePopulationCohorts
              parameters:
                scope_id: $response.body#/id
            populationExclusionCohorts:
              operationId: getScopePopulationExclusionCohorts
              parameters:
                scope_id: $response.body#/id
            payloadOutcomes:
              operationId: getScopePayloadOutcomes
              parameters:
                scope_id: $response.body#/id
            payloadPersonaSets:
              operationId: getScopePayloadPersonaSets
              parameters:
                scope_id: $response.body#/id