Request fields by grib code instead of long name



Hello,



I'm converting some old webapi request to cdsapi ones (from ADS). In my previous requests, I was using the grib codes. Is there a way to use the grib codes of the variables instead of their long names? I tried a few options of syntax but couldn't make it work.


Working cdsapi request with the long name:


```python

import cdsapi
import yaml

with open('/home/Earth/pbretonn/.adsapirc', 'r') as f:
            credentials = yaml.safe_load(f)

c = cdsapi.Client(url=credentials['url'], key=credentials['key'])

c.retrieve(
    'cams-global-fire-emissions-gfas',
    {
        'date': '2022-08-08/2022-08-08',
        'format': 'grib',
        'variable': 'wildfire_flux_of_organic_carbon',
    },
    'download.grib')

```

Old request with the grib codes:

```python

from ecmwfapi import ECMWFDataServer
import os

server = ECMWFDataServer()
server.retrieve({
         "class": "mc",
         "dataset": "cams_gfas",
         "date": "_date_" ,
         "expver": "0001",
         "levtype": "sfc",
         "param": "90.210",
         "step": "0-24",
         "stream": "gfas",
         "time": "00:00:00",
         "type": "ga",
         "target": "download.grib",
     })
```


What I can't make work is something like:

```python

import cdsapi
import yaml

with open('/home/Earth/pbretonn/.adsapirc', 'r') as f:
            credentials = yaml.safe_load(f)

c = cdsapi.Client(url=credentials['url'], key=credentials['key'])

c.retrieve(
    'cams-global-fire-emissions-gfas',
    {
        'date': '2022-08-08/2022-08-08',
        'format': 'grib',
        'variable': ''90.210",
    },
    'download.grib')
```

If the option is not available, I wanted to build a dictionary based on the grib codes and their equivalent long names (this is just an example request, but I have a long list of codes to convert), but I'm actually not sure where the names of the variables of the cdsapi come from.



Thank you!