This patch drops the catalog table _timescaledb_catalog.hypertable_compression
and stores those settings in _timescaledb_catalog.compression_settings instead.
The storage format is changed and the new table will have 1 entry per relation
instead of 1 entry per column and has no dependancy on hypertables.
All other aspects of compression will remain the same. This is refactoring is
to enable per chunk compression settings in a follow-up patch.