Support Root Resource query

Apparently, it is possible to query resources from the root endpoint:

Section [3.4.2.1. Query Endpoints](https://datatracker.ietf.org/doc/html/rfc7644#section-3.4.2.1) says:

> Queries MAY be performed against a SCIM resource object, a type endpoint, **or a SCIM server root**

(emphasis mine)

Also:

> A query against a server root indicates that all resources within the
> server SHALL be included, subject to filtering. A filter expression
> using "meta.resourceType" MAY be used to restrict results to one or
> more specific resource types (to exclude others)

As far as I can see (but I could be wrong), there's no implementation of the root endpoint yet. Is it something that's planned?

Start at the SCIM server root endpoint and compare its query handling with RFC 7644 §3.4.2.1. Done means root queries include all resources, honor filtering, and allow a meta.resourceType filter to restrict resource types.

Written by the indexing model from the issue text.