itit-18 and 43 with option only to use the Initiating Gateway

[oliveregger]

for https://ikit.cara.ch/docs/changelog/ we need to update the option that if no
Registry / Repositoy is provided we use only the Initiating Gateway as an end point.

XDS: ITI-18/43 Requests to Initiating Gateway sufficient (no Document Registry / Repository calls necessary)
An ITI-18 Query to the Initiating Gateway will return all document entries in all communities including document entries in the community of the Initiating Gateway. This means a separate request to the ITI-18 registry is not necessary, or otherwise duplicates would need to be filtered out. Equivalent an ITI-43 retrieve to the Initiating Gateway can handle also document retrieve within the own community, not only for the external communities.