Reduce amount of indexes when using `viur-core>=3.6`

[phorward]

Hi!

viur-scriptor currently requires further indexes when used within a project that uses viur-core>=3.6. This is because v3.6 comes with the default_order features.

The additionally required indexes are:

- kind: viur-script-node
  properties:
  - name: plugin
  - name: sortindex

- kind: viur-script-leaf
  properties:
  - name: plugin
  - name: sortindex

This seems wrong, as the only required index before was, and still should be enough:

- kind: viur-script-leaf
  properties:
  - name: parententry
  - name: sortindex

- kind: viur-script-node
  properties:
  - name: parententry
  - name: sortindex

The newly added indexes are required by viur-core>=3.6 projects, but shouldn't!

Therefore, two proposals:

1. Simple but ugly: Try to run the current request with the parententry to the root node, this should avoid the requirement for an index on the plugin property
2. Otherwise, enhanced but better: Just request the script's node tree as already done, and check there for plugin=True setting, which will also reduce the amount of requests in the end. Nodes with plugin=True will be handled differently in this case.

The second proposal is the better option.