Support and display series attributes

Discussed in dbnomics-fetchers/management#156 (comment 8163)

There exist characteristics of a series that are described by dimensions by that have only one value. This information is useful to understand a series but are useless as facet.

Acceptation criteria

• It needs to be added to the data model in order to be usable by new fetchers
• Series attributes MUST be returned by the API
• Series attributes MUST be displayed in the UI but not be used as facet
• Series attributes MUST be available as DataFrame columns in Python client

Questions

• What about R client?

Examples

• dbnomics-fetchers/management#445 (closed) IMF/IFS/A.7A.HPU_XDR: website, API, series.jsonl (big)

{
    "attributes": {
        "TIME_FORMAT": "P1Y",
        "UNIT_MULT": "6"
    },
    "code": "A.1C_355.BCAXF_BP6_USD",
    "dimensions": {
        "FREQ": "A",
        "INDICATOR": "BCAXF_BP6_USD",
        "REF_AREA": "1C_355"
    },
    "name": "Annual – Curacao & St. Maarten – Balance of Payments, Supplementary Items, Current Account, Net (excluding exceptional financing), US Dollars, Millions",
    "observations": ...
}