Connection-less data cube creation

[soxofaan]

Coincidentally I got two requests this week how to start with a datacube (from load_collection or load_stac) without an actual connection.

DataCube has a load_collection factory to make that possible

import openeo

cube = openeo.DataCube.load_collection(
    "FOO_S2",
    temporal_extent=["2024-09-01", "2024-10-01"],
    # ...
    fetch_metadata=False,
)

Unfortunately this currently requires that fetch_metadata=False, which should not be necessary.

For load_stac it's a bit uglier at the moment:

import openeo.rest.datacube

arguments = {
    # ...
}

cube = openeo.rest.datacube.DataCube(
    openeo.rest.datacube.PGNode("load_stac", arguments=arguments),
    connection=None,
)

given the importance of load_stac, we should add a factory for that one too