storage: always schedule adjacent segment compaction

We previously fell back on adjacent segment compaction only if there was
no new data to compact. In some situations, we've seen the rate of
incoming data outpace the compaction interval, causing segments to pile
up without ever being merged.

This change tweaks the logic to always run adjacent segment compaction
after running sliding window compaction.

src/v/storage/disk_log_impl.cc

@@ -1316,11 +1316,13 @@ ss::future<> disk_log_impl::do_compact(
         std::rethrow_exception(eptr);
     }
     bool compacted = did_compact_fut.get();
-    if (!compacted) {
-        // If sliding window compaction did not occur, we fall back to adjacent
-        // segment compaction.
-        co_await compact_adjacent_segments(compact_cfg);
-    }
+    vlog(
+      gclog.debug,
+      "Sliding compaction of {} did {}compact data, proceeding to adjacent "
+      "segment compaction",
+      config().ntp(),
+      compacted ? "" : "not ");
+    co_await compact_adjacent_segments(compact_cfg);
 }
 
 ss::future<> disk_log_impl::gc(gc_config cfg) {