Merge patient_id with FSS filter

[rcdilorenzo]

The patient_id argument needs to merge just like with the must FSS query.

phc.Observation.get_data_frame(patient_id="41e6a5bc-7b8a-4434-b38b-0da652d6364e", query_overrides={
    "where": {
        "type": "elasticsearch",
        "query": {
            "bool": {
                "filter": [
                    {"term": {"code.coding.system.keyword": "http://my-system-example.org"}},
                    {"term": {"code.coding.code.keyword": "123456-7"}}
                ]
            }
        }
    }
})