Update bucket settings to be compatible with dp9 and not set defaults for optional fields

[DemetrisChr]

Change

• All fields in BucketSettings are optional apart from name. Don't set default values on them as the core now does not send unset fields to the server. Rely on the core's default value for the RAM quota. Update cb_generate_bucket_settings to reflect these
• replica_indexes and flush_enabled are now optional booleans in the core. In cb_extract_bucket_settings use their value to set the corresponding Ruby attributes, as an std::optional<bool> is truthy if the value is set (either to true or false)
• Update bucket history retention test to expect that bytes/duration default to nil if the bucket does not support history retention

[cb-sdk-robot]

Can one of the admins verify this patch?