Called from try_flush_memtable_to_sstable,
maybe_wait_for_sstable_count_reduction will wait for
compaction to catch up with memtable flush if there
the bucket to compact is inflated, having too many
sstables. In that case we don't want to add fuel
to the fire by creating yet another sstable.
Fixes#4116Closes#10954
* github.com:scylladb/scylla:
table: Add test where compaction doesn't keep up with flush rate.
compaction_manager: add maybe_wait_for_sstable_count_reduction
time_window_compaction_strategy: get_sstables_for_compaction: clean up code
time_window_compaction_strategy: make get_sstables_for_compaction idempotent
time_window_compaction_strategy: get_sstables_for_compaction: improve debug messages
leveled_manifest: pass compaction_counter as const&