We make the `CDC_GENERATIONS_V3` table single-partition and change the
clustering key from `range_end` to `(id, range_end)`. We also change the
type of `id` to `timeuuid` and ensure that a new generation always has
the highest `id`. These changes allow efficient clearing of obsolete CDC
generation data, which we need to prevent Raft-topology snapshots from
endlessly growing as we introduce new generations over time.
All this code is protected by an experimental feature flag. It includes
the definition of `CDC_GENERATIONS_V3`. The table is not created unless
the feature flag is enabled.
Fixes#15163Closes#15319
* github.com:scylladb/scylladb:
system_keyspace: rename cdc_generation_id_v2
system_keyspace: change id to timeuuid in CDC_GENERATIONS_V3
cdc: generation: remove topology_description_generator
cdc: do not create uuid in make_new_generation_data
system_kayspace: make CDC_GENERATIONS_V3 single-partition
cdc: generation: introduce get_common_cdc_generation_mutations
cdc: generation: rename get_cdc_generation_mutations
a184b07cbb