Query nested relations recursively

Suggestion

Original from comment.

LoopBack 4 provides the custom scope to achieve inclusion, which was implemented in #3454. But it only goes down to the certain levels of relations that are described in the filter, for example, three levels:

    const filter = {
      include: [
        {
          relation: 'nested 1',
          scope: {
            include: [{relation: 'nested 2'}],
          },
        },
      ],
    };

It'd be good to have a better way to query nested relations to max depth/ N degrees, something like {relation: "nested", depth: 10}.

Examples

Model Comment has many replies: Comment[], and comments in the replies has many replies, etc. Returns when there is no more replies or the max depth is reached.

Acceptance criteria

• Provide a way to query nested relations to max depth/ N degrees, or at least to have a helper function for writing the filter.
• Should document how to configure the max depth of such traverses.

Beginne mit der Arbeit zur Einbeziehung von custom-scope in Issue #3454 und den Beispielen für nested-relation-Filter in diesem Issue. Lege fest, wie sich eine tiefenbegrenzte Traversierung für rekursive Comment-Antworten verhalten soll, dokumentiere die max-depth-Konfiguration und überprüfe, dass die Traversierung entweder am Limit oder am Ende der Relation stoppt.