ALTER of the sharded table

[donhardman]

We should add support for altering sharded tables.
Currently, there is no alter supported on the distributed table, so we can catch it with Buddy and process the logic.
Altering a sharded table should drop the distributed table, alter all sharded tables, and once it's done, create the distributed table again.
As discussed before, the application should protect writing on its own. When we remove the distributed table, it will get an error, which is totally fine.