storage: expose disk_log_builder::feature_table

This will be useful to test methods that need a feature table (e.g.
deduplicate_segments() has a feature table as an argument).

(cherry picked from commit 958aaf7)

src/v/storage/tests/utils/disk_log_builder.h

@@ -376,6 +376,10 @@ class disk_log_builder {
 
     void set_time(model::timestamp t) { _ts_cursor = t; }
 
+    ss::sharded<features::feature_table>& feature_table() {
+        return _feature_table;
+    }
+
 private:
     template<typename Consumer>
     auto consume_impl(Consumer c, log_reader_config config) {