cluster: upgrade to v.7 creates cluster_uuid

New feature `seeds_driven_bootstrap_capable` to control cluster upgrade.
Raft0 leader issues `bootstrap_cluster_cmd` if controller log is
non-empty and no cluster_uuid. This is done in a detached fiber
waiting on the new feature to be enabled.

src/v/cluster/controller.cc

@@ -521,6 +521,11 @@ ss::future<> controller::create_cluster() {
     }
 }
 
+bool controller::controller_log_exists() const {
+    return _raft0->last_visible_index() > model::offset{}
+           || _raft0->config().brokers().size() > 1;
+}
+
 /**
  * This function provides for writing the controller log immediately
  * after it has been created, before anything else has been written
@@ -537,10 +542,29 @@ ss::future<> controller::cluster_creation_hook(cluster_discovery& discovery) {
         vassert(
           config::node().seed_servers().empty(), "We are not on the root node");
 
-        if (
-          _raft0->last_visible_index() > model::offset{}
-          || _raft0->config().brokers().size() > 1) {
+        if (controller_log_exists()) {
             // The controller log has already been written to
+            if (!_storage.local().get_cluster_uuid()) { // HERE: ctrllog done?
+                // No cluster UUID - we are upgrading an existing cluster
+                vlog(
+                  clusterlog.info,
+                  "Cluster will be upgraded once all nodes are upgraded");
+                ssx::background
+                  = _feature_table.local()
+                      .await_feature(
+                        features::feature::seeds_driven_bootstrap_capable,
+                        _as.local())
+                      .then([this] { return create_cluster(); })
+                      .then([] {
+                          vlog(clusterlog.info, "Cluster has been upgraded");
+                      })
+                      .handle_exception([](const std::exception_ptr e) {
+                          vlog(
+                            clusterlog.warn,
+                            "Error upgrading the cluster. {}",
+                            e);
+                      });
+            }
             co_return;
         }
 
@@ -572,9 +596,7 @@ ss::future<> controller::cluster_creation_hook(cluster_discovery& discovery) {
         co_return;
     }
 
-    if (
-      _raft0->last_visible_index() > model::offset{}
-      || _raft0->config().brokers().size() > 1) {
+    if (controller_log_exists()) {
         // The controller log has already been written to
         // TODO: create_cluster() but use the metrics' cluster_id
     }

src/v/cluster/controller.h

@@ -152,6 +152,8 @@ class controller {
      */
     ss::future<> create_cluster();
 
+    bool controller_log_exists() const;
+
     ss::future<> cluster_creation_hook(cluster_discovery& discovery);
 
     config_manager::preload_result _config_preload;

src/v/features/feature_table.cc

@@ -51,6 +51,8 @@ std::string_view to_string_view(feature f) {
         return "replication_factor_change";
     case feature::ephemeral_secrets:
         return "ephemeral_secrets";
+    case feature::seeds_driven_bootstrap_capable:
+        return "seeds_driven_bootstrap_capable";
     case feature::test_alpha:
         return "__test_alpha";
     }

src/v/features/feature_table.h

@@ -46,6 +46,7 @@ enum class feature : std::uint64_t {
     node_id_assignment = 0x1000,
     replication_factor_change = 0x2000,
     ephemeral_secrets = 0x4000,
+    seeds_driven_bootstrap_capable = 0x8000,
 
     // Dummy features for testing only
     test_alpha = uint64_t(1) << 63,
@@ -188,6 +189,12 @@ constexpr static std::array feature_schema{
     feature::ephemeral_secrets,
     feature_spec::available_policy::always,
     feature_spec::prepare_policy::always},
+  feature_spec{
+