Bring back settings holder EnableFeature because we need it for the transactional session (#7452)

Co-authored-by: Daniel Marbach <danielmarbach@users.noreply.github.com>

Author: danielmarbach

src/NServiceBus.Core.Tests/ApprovalFiles/APIApprovals.ApproveNServiceBus.approved.txt

@@ -1329,6 +1329,8 @@ namespace NServiceBus.Features
     }
     public static class SettingsExtensions
     {
+        public static void EnableFeature<T>(this NServiceBus.Settings.SettingsHolder settings)
+            where T : NServiceBus.Features.Feature { }
         [System.Obsolete("It is no longer possible to enable features by default on the settings. Features " +
             "can enable other features by calling EnableByDefault<T> in the constructor. Will" +
             " be removed in version 11.0.0.", true)]

src/NServiceBus.Core/Features/EndpointConfigurationExtensions.cs

@@ -17,7 +17,7 @@ public static partial class EndpointConfigurationExtensions
     public static void EnableFeature<T>(this EndpointConfiguration config) where T : Feature
     {
         ArgumentNullException.ThrowIfNull(config);
-        config.Settings.Get<FeatureComponent.Settings>().EnableFeature<T>();
+        config.Settings.EnableFeature<T>();
     }
 
     /// <summary>

src/NServiceBus.Core/Features/SettingsExtensions.cs

@@ -10,6 +10,14 @@ namespace NServiceBus.Features;
 /// </summary>
 public static partial class SettingsExtensions
 {
+    /// <summary>
+    /// Enables the given feature.
+    /// </summary>
+    /// <remarks>Enabling features is intended to be used for downstream components that only have access to settings. Features that need to enable other features should use <see cref="Feature.EnableByDefault{T}"/>.</remarks>
+    /// <typeparam name="T">The feature to enable.</typeparam>
+    public static void EnableFeature<T>(this SettingsHolder settings) where T : Feature
+        => settings.Get<FeatureComponent.Settings>().EnableFeature<T>();
+
     /// <summary>
     /// Returns if a given feature has been activated in this endpoint.
     /// </summary>