Remove strict check over Storage Tiers

[Aeris1One]

There's a strict check over which storage tiers entries are allowed.
This can be problematic when providers have their own storage tiers (as an example, Scaleway provides the "ONEZONE_IA" storage tier for single-AZ data)

Here's the related code :

synapse-s3-storage-provider/s3_storage_provider.py

Line 44 in 6f8b382

_VALID_STORAGE_CLASSES = (

synapse-s3-storage-provider/s3_storage_provider.py

Line 163 in 6f8b382

assert storage_class in _VALID_STORAGE_CLASSES