Currently the major compaction task impl grabs this (non-updateable)
value from db::config. That's not good, all services including
compaction manager have their own configs from which they take options.
Said that, this patch puts the said option onto
compaction_manager::config, makes use of it and configures one from
db::config on start (and tests).
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Closesscylladb/scylladb#20174