[sensorthings] Add support for Multidatastreams (Request in QGIS)

[qgis-bot]

Request for documentation

From pull request qgis/QGIS#56958
Author: @nyalldawson
QGIS version: 3.38

[sensorthings] Add support for Multidatastreams

PR Description:

This adds support for the Multidatastream entity type, as implemented in the SensorThings version 1.1 "MultiDatastream extension"

While the specification mandates that MultiDatastreams have an optional polygon geometry, I've encountered numerous servers which expose different geometry types for this entity or which return errors when attempting to read the geometries from MultiDatastreams. Accordingly we always expose an option to load MultiDatastreams as geometryless layers alongside the default option to load them as polygon layers, to handle a wider range of connections.

Commits tagged with [need-docs] or [FEATURE]