in this series, we try to use `generation_type` as a proxy to hide the consumers from its underlying type. this paves the road to the UUID based generation identifier. as by then, we cannot assume the type of the `value()` without asking `generation_type` first. better off leaving all the formatting and conversions to the `generation_type`. also, this series changes the "generation" column of sstable registry table to "uuid", and convert the value of it to the original generation_type when necessary, this paves the road to a world with UUID based generation id.
Closes#13652
* github.com:scylladb/scylladb:
db: use uuid for the generation column in sstable registry table
db, sstable: add operator data_value() for generation_type
db, sstable: print generation instead of its value
48b9f31a08