Accept series code masks in "/series?series_ids" endpoint
Context
In dbnomics-fetchers/ine-spain-fetcher@b53bf463 we changed the series codes from generated ones based on dimension codes (e.g.72.b101.311118.n.s1.00.euros), to INE-SPAIN provided ones (e.g. CTNFSI6514). This is because we spotted a bug: some generated dimension codes corresponded to many series, which is not acceptable since a series code must be unique. Using INE-SPAIN provided series codes solved that issue.
However using the generated series codes should still work. Indeed, the web page at URL https://db.nomics.world/INE-SPAIN/30906/72.b101.311118.n.s1.00.euros opens correctly the series CTNFSI6514, and the URL https://db.nomics.world/INE-SPAIN/30906/CTNFSI6514 works too. In the same vein, the API URL https://api.db.nomics.world/v22/series/INE-SPAIN/30906/72.b101.311118.n.s1.00.euros is equivalent to the URL https://api.db.nomics.world/v22/series/INE-SPAIN/30906/CTNFSI6514
Bug: the API URL "/series?series_ids=" does not accept both forms: https://api.db.nomics.world/v22/series?series_ids=INE-SPAIN%2F30906%2F72.b101.311118.n.s1.00.euros does not return anything, but https://api.db.nomics.world/v22/series?series_ids=INE-SPAIN%2F30906%2FCTNFSI6514 does.