feature: grandfather ME_SSTABLE feature

"me" format sstables were introduced in d370558279 (Jan 2022; 5.1)
and so can be assumed always present. The listener that checks when
the cluster understands ME_SSTABLE was removed and in its place
we default to sstable_version_types::me (and call on_enabled()
immediately).

db/sstables-format-selector.cc

@@ -85,7 +85,7 @@ future<> sstables_format_listener::start() {
     assert(this_shard_id() == 0);
     // The listener may fire immediately, create a thread for that case.
     co_await seastar::async([this] {
-        _features.local().me_sstable.when_enabled(_me_feature_listener);
+        _me_feature_listener.on_enabled();
     });
 }
 

db/sstables-format-selector.hh

@@ -47,7 +47,7 @@ public:
 class sstables_format_selector {
     sharded<replica::database>& _db;
     db::system_keyspace* _sys_ks = nullptr;
-    sstables::sstable_version_types _selected_format = sstables::sstable_version_types::mc;
+    sstables::sstable_version_types _selected_format = sstables::sstable_version_types::me;
     future<> select_format(sstables::sstable_version_types new_format);
     future<> read_sstables_format();
 public:

gms/feature_service.cc

@@ -134,6 +134,7 @@ std::set<std::string_view> feature_service::supported_feature_set() const {
         "COMPUTED_COLUMNS"sv,
         "SCHEMA_COMMITLOG"sv,
         "MD_SSTABLE_FORMAT"sv,
+        "ME_SSTABLE_FORMAT"sv,
     };
 
     if (is_test_only_feature_deprecated()) {

gms/feature_service.hh

@@ -81,7 +81,6 @@ public:
 
 public:
     gms::feature user_defined_functions { *this, "UDF"sv };
-    gms::feature me_sstable { *this, "ME_SSTABLE_FORMAT"sv };
     gms::feature view_virtual_columns { *this, "VIEW_VIRTUAL_COLUMNS"sv };
     gms::feature digest_insensitive_to_expiry { *this, "DIGEST_INSENSITIVE_TO_EXPIRY"sv };
     gms::feature cdc { *this, "CDC"sv };