Store or update an item.

curl --location --request PUT 'http://127.0.0.1:2024/store/items' \
--header 'x-api-key: <api-key>' \
--header 'Content-Type: application/json' \
--data-raw '{
    "namespace": [
        "string"
    ],
    "key": "string",
    "value": {}
}'