Generic API client: include parent fields in child resource

[willi-mueller]

Tell us what you do here

• implementing verified source (please link a relevant issue labeled as verified source)
• fixing a bug (please link a relevant bug report)
• improving, documenting, or customizing an existing source (please link an issue or describe below)
• anything else (please link an issue or describe below)

Relevant issue

issue #313

More PR info

This PR allows adding arbitrary fields from the parent resource in the child resource. Example: In Workable, jobs/{shortcode}/recruiters does not include the jobs shortcode. Thus, the response does not tell to which job a recruiter belongs.

For example, a child resource can be specified as follows in order to include confidential and id from the jobs resource in the jobs_id_approval_flows resource:

"jobs/{id}/approval_flows": {
  "params": {
      "id": ResolveConfig("jobs", "id"),
  },
  "resource": {**default_resource_config, "include_from_parent": ["confidential", "id"]},
}

The resulting fields in the child resource are _jobs_confidential and _jobs_id.

Validation

Marked yellow: The parent's resource name is the prefix for its field in the child. This is to avoid name collisions.
Marked green & blue: the field names of the parent are the field names in the child:

Data is loaded. Note that id and _jobs_id are identical which proves that the correct values are taken from the parent record: