feat: keywords usage in product_types configuration

[sbrunato]

• new field keywords added in product types configuration file product_types.yml. Field is case insensitive and ignores - or _ characters
• whoosh product types search index is now rebuilt when product_types.yml MD5 checksum changes instead of eodag version.

This enables the following behavior:

>>> from eodag import EODataAccessGateway
>>> dag = EODataAccessGateway()
>>> dag.guess_product_type(keywords="sentinel* SAFE")
['S1_SAR_GRD', 'S1_SAR_OCN', 'S1_SAR_RAW', 'S1_SAR_SLC', 'S2_MSI_L1C', 'S2_MSI_L2A']
>>> dag.guess_product_type(keywords="landsat* Collection2")
['LANDSAT_C2L1', 'LANDSAT_C2L2ALB_BT', 'LANDSAT_C2L2ALB_SR', 'LANDSAT_C2L2ALB_ST', 'LANDSAT_C2L2ALB_TA', 'LANDSAT_C2L2_SR', 'LANDSAT_C2L2_ST']
>>> dag.guess_product_type(keywords="landsat* Collection2 L1")
['LANDSAT_C2L1']
>>> dag.search(keywords="landsat* Collection2 L1")
# will perform search on LANDSAT_C2L1
>>> dag.guess_product_type(keywords="cog")
['S2_MSI_L2A_COG']
>>> dag.search(keywords="cog")
# will perform search on S2_MSI_L2A_COG

[sbrunato]

fixes #165