There was an attempt to cut feature-service -> system-keyspace dependency (#13172) which turned out to require more changes. Here's a preparation squeezing from this future work.
This set
- leaves only batch-enabling API in feature service
- keeps the need for async context in feature service
- narrows down system keyspace features API to only load and store records
- relaxes features updating logic in sys.ks.
- cosmetic
Closes#13264
* github.com:scylladb/scylladb:
feature_service: Indentation fix after previous patch
feature_service: Move async context into enable()
system_keyspace: Refactor local features load/save helpers
feature_service: Mark supported_feature_set() const
feature_service: Remove single feature enabling method
boot: Enable features in batch
gossiper: Enable features in batch
c54a3d9c10