Fixes#14668
In #14668, we have decided to introduce a new `scylla.yaml` variable for the schema commitlog segment size and set it to 128MB. The reason is that segment size puts a limit on the mutation size that can be written at once, and some schema mutation writes are much larger than average, as shown in #13864. This `schema_commitlog_segment_size_in_mb variable` variable is now added to `scylla.yaml` and `db/config`.
Additionally, we do not derive the commitlog sync period for schema commitlog anymore because schema commitlog runs in batch mode, so it doesn't need this parameter. It has also been discussed in #14668.
Closes#14704
* github.com:scylladb/scylladb:
replica: do not derive the commitlog sync period for schema commitlog
config: set schema_commitlog_segment_size_in_mb to 128
config: add schema_commitlog_segment_size_in_mb variable