Merge a patch series from Piotr Jastrzębski (haaawk):
This PR introduces CDC in it's minimal version.
It is possible now to create a table with CDC enabled or to enable/disable
CDC on existing table. There is a management of CDC log and description
related to enabling/disabling CDC for a table.
For now only primary key of the changed data is logged.
To be able to co-locate cdc streams with related base table partitions it
was needed to propagate the information about the number of shards per node.
This was node through gossip.
There is an assumption that all the nodes use the same value for
sharding_ignore_msb_bits. If it does not hold we would have to gossip
sharding_ignore_msb_bits around together with the number of shards.
Fixes#4986.
Tests: unit(dev, release, debug)
631846a852