Missing SEVIRI service mode for new IODC sub-satellite longitude of MET09

[strandgren]

Describe the bug
The new service mode of MET09 (IODC at 45.5 degrees East) is not included in

satpy/satpy/readers/eum_base.py

Line 89 in df8ddd1

def get_service_mode(instrument_name, ssp_lon):

leading to errors when reading SEVIRI L2 bufr data with area definition (reader_kwargs={'with_area_definition': True})

To Reproduce

from satpy import Scene

sev_l2_bufr_file = '<filename>'
scn = Scene(filenames=[sev_l2_bufr_file], reader='seviri_l2_bufr', reader_kwargs={'with_area_definition': True)
scn.load(['ki'])

Expected behavior
Successfully load the data and resample onto the original 2D grid.

Actual results

INFO yaml_reader.py Line 1005: Dataset longitude is missing the area attribute and will not be flipped.
INFO yaml_reader.py Line 1005: Dataset latitude is missing the area attribute and will not be flipped.
WARNING yaml_reader.py Line 700: Failed to load DataID(name='ki', resolution=9001.209497451, modifiers=()) from <SeviriL2BufrFileHandler: '/tcenas/fbf/mpef/store/OPEB/GIIBUFRProduct/GIIBUFRProduct_20221101120000Z_00_OMPEFS02_MET09_FES_E0455'>
Traceback (most recent call last):
  File "/tcenas/home/strandgren/git/ext/py/satpy/latest/satpy/satpy/readers/yaml_reader.py", line 695, in _load_dataset
    projectable = fh.get_dataset(dsid, ds_info)
  File "/tcenas/home/strandgren/git/ext/py/satpy/latest/satpy/satpy/readers/seviri_l2_bufr.py", line 204, in get_dataset
    xarr = self.get_dataset_with_area_def(arr, dataset_id)
  File "/tcenas/home/strandgren/git/ext/py/satpy/latest/satpy/satpy/readers/seviri_l2_bufr.py", line 226, in get_dataset_with_area_def
    self._area_def = self._construct_area_def(dataset_id)
  File "/tcenas/home/strandgren/git/ext/py/satpy/latest/satpy/satpy/readers/seviri_l2_bufr.py", line 267, in _construct_area_def
    stand_area_def = get_area_def(area_naming['area_id'])
  File "/tcenas/home/strandgren/git/ext/py/satpy/latest/satpy/satpy/resample.py", line 223, in get_area_def
    return parse_area_file(get_area_file(), area_name)[0]
  File "/tcenas/proj/optcalimg/strandgren/miniconda3/envs/pysat_latest/lib/python3.8/site-packages/pyresample/area_config.py", line 138, in parse_area_file
    return _parse_yaml_area_file(area_file_name, *regions)
  File "/tcenas/proj/optcalimg/strandgren/miniconda3/envs/pysat_latest/lib/python3.8/site-packages/pyresample/area_config.py", line 191, in _parse_yaml_area_file
    raise AreaNotFound('Area "{0}" not found in file "{1}"'.format(area_name, area_file_name))
pyresample.area_config.AreaNotFound: 'Area "msg_seviri_unknown_9km_ext" not found in file "[\'/tcenas/home/strandgren/git/ext/py/satpy/latest/satpy/satpy/etc/areas.yaml\', \'/tcenas/home/strandgren/git/eum/py/local_readers/areas.yaml\']"'
ERROR yaml_reader.py Line 849: Could not load dataset 'DataID(name='ki', resolution=9001.209497451, modifiers=())': "Could not load DataID(name='ki', resolution=9001.209497451, modifiers=()) from any provided files"
Traceback (most recent call last):
  File "/tcenas/home/strandgren/git/ext/py/satpy/latest/satpy/satpy/readers/yaml_reader.py", line 847, in _load_dataset_with_area
    ds = self._load_dataset_data(file_handlers, dsid, **kwargs)
  File "/tcenas/home/strandgren/git/ext/py/satpy/latest/satpy/satpy/readers/yaml_reader.py", line 719, in _load_dataset_data
    proj = self._load_dataset(dsid, ds_info, file_handlers, **kwargs)
  File "/tcenas/home/strandgren/git/ext/py/satpy/latest/satpy/satpy/readers/yaml_reader.py", line 704, in _load_dataset
    raise KeyError(
KeyError: "Could not load DataID(name='ki', resolution=9001.209497451, modifiers=()) from any provided files"
WARNING scene.py Line 1276: The following datasets were not created and may require resampling to be generated: DataID(name='ki', resolution=9001.209497451, modifiers=())
INFO view.py Line 76:  Generating plotting window and visualizing requested satellite data.
Traceback (most recent call last):
  File "/tcenas/home/strandgren/git/ext/py/satpy/latest/satpy/satpy/dataset/data_dict.py", line 169, in __getitem__
    return super(DatasetDict, self).__getitem__(item)
KeyError: 'ki'

Additional context
To be fixed by @strandgren during PCW in Athens. This fix will also include modifying the MSG IODC area definitions in areas.yaml to match the current sub-satellite longitude of MET09 (45.5 degrees North). This will be a temporary work-around until #2238 has been realized.