Update outdated search syntax in demo Notebooks

[sadielbartholomew]

Whilst exploring the capabilities of Datapoint through the demo Jupyter Notebooks I found that a code cell would fail with an IndexError because the collect_cloud_assets() would return zero products when at least three were expected, for example for the demo/basic_usage.ipynb Notebook I got 0 products with the search as-is:

>>> search_basic = client.search(
    collections=['cmip6'],
    query=[
        'experiment_id=ssp585',
        'activity_id=ScenarioMIP',
        'institution_id=KIOST',
    ],
    max_items = 10
)
>>> cluster = search_basic.collect_cloud_assets()
>>> cluster
<DataPointCluster: CEDA-333146-139631-409864 (Datasets: 0)>
 - url: https://api.stac.ceda.ac.uk/
 - organisation: CEDA
 - search_terms: {'query': ['experiment_id=ssp585', 'activity_id=ScenarioMIP', 'institution_id=KIOST'], 'max_items': 10}
 - collections: ['cmip6']
 - products: 0
Products:

@dwest77a clarified that this isn't expected and is a result of the search query using syntax which is deprecated so does now return the expected results.

The Notebooks should be updated so that the cells run through successfully. I will put in a PR since I am using these for guidance so it is handy for me to get these in updated working form ASAP.