Handle Sentinel-3 SLSTR stripe changes

[AndreaBrg]

It appears that starting from 2020-01-14 the SLSTR product changed from i to f stripes for at least the F1 band. This breaks the reader when the F1 band is requested.

It seems that the newer items are marked with the 004 version suffix, the older with 003. This can be used to identify the correct reader.

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Extra:
There is a "transition" period where both version of an item are provided, e.g.

S3B_SL_1_RBT____20200113T105031_20200113T105331_20200812T083716_0180_034_208_1620_LR1_R_NT_004 has i: False has_f: True
S3B_SL_1_RBT____20200113T105031_20200113T105331_20200114T154925_0179_034_208_1620_LN2_O_NT_003 has i: True has_f: False

This will lead to duplicate items and geotiffs when products in this period are requested. We should evaluate if filtering them somewhere is useful.