Merge branch 'hotifx/add_test_processing_site_fixture' into 'main'

Add processing site

See merge request !46

ldvspec/fixtures/test-env.json

+[{"model": "lofardata.atdbprocessingsite", "pk": "Test", "fields": {"url": "https://sdc-dev.astron.nl:5554/atdb/", "access_token": "69dacb47030d0dc7ef412ee53765c5066adeeee4"}}, {"model": "lofardata.dataproductfilter", "pk": 1, "fields": {"field": "obs_id", "name": "SAS Id", "lookup_type": "exact", "filter_type": "Free"}}]
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