Returning several entities in REST API response

[CasperWA]

In connection with the PR to add a /querybuilder-endpoint to the REST API (#4337), the response is hacked together to be able to return multiple entries (using multiple tags), where the "normal" response for the REST API is built to return only a single tag/resource entry type, e.g., a specific Node type, Groups, etc. (See this comment).

As stated by @ltalirz in the comment, it would be good to incorporate this method of collating the QueryBuilder responses in a single REST API response, in an utility function upstream in the code, instead of having it as a "hack" in the request method.
This is especially true for any upcoming endpoints that will utilize the similar multi-entry type-responses.