Use FF to get node disposal strategy

src/ApiService/ApiService/FeatureFlags.cs

@@ -2,4 +2,5 @@
 
 public static class FeatureFlagConstants {
     public const string EnableScribanOnly = "EnableScribanOnly";
+    public const string EnableNodeDecommissionStrategy = "EnableNodeDecommissionStrategy";
 }

src/ApiService/ApiService/ServiceConfiguration.cs

@@ -38,8 +38,6 @@ public interface IServiceConfig {
     public string? OneFuzzMonitor { get; }
     public string? OneFuzzOwner { get; }
 
-    public string OneFuzzNodeDisposalStrategy { get; }
-
     public string? OneFuzzResourceGroup { get; }
     public string? OneFuzzTelemetry { get; }
 
@@ -135,8 +133,6 @@ public string OneFuzzVersion {
     }
 
     public string? OneFuzzAllowOutdatedAgent => GetEnv("ONEFUZZ_ALLOW_OUTDATED_AGENT");
-
-    public string OneFuzzNodeDisposalStrategy { get => GetEnv("ONEFUZZ_NODE_DISPOSAL_STRATEGY") ?? "scale_in"; }
     public string OneFuzzStoragePrefix => ""; // in production we never prefix the tables
 
     public Uri OneFuzzBaseAddress {

src/ApiService/ApiService/onefuzzlib/ScalesetOperations.cs

@@ -608,11 +608,7 @@ where x.State.ReadyForReset()
         }
 
         // Perform operations until they fail due to scaleset getting locked:
-        var strategy = _context.ServiceConfiguration.OneFuzzNodeDisposalStrategy.ToLowerInvariant() switch {
-            // allowing typo’d or correct name for config setting:
-            "decomission" or "decommission" => NodeDisposalStrategy.Decommission,
-            _ => NodeDisposalStrategy.ScaleIn,
-        };
+        var strategy = await _context.FeatureManagerSnapshot.IsEnabledAsync(FeatureFlagConstants.EnableNodeDecommissionStrategy) ? NodeDisposalStrategy.Decommission : NodeDisposalStrategy.ScaleIn;
 
         var reimageNodes = await ReimageNodes(scaleSet, toReimage.Values, strategy);
         if (!reimageNodes.IsOk) {

src/ApiService/IntegrationTests/Fakes/TestServiceConfiguration.cs

@@ -58,8 +58,6 @@ public TestServiceConfiguration(string tablePrefix) {
 
     public string? OneFuzzOwner => throw new System.NotImplementedException();
 
-    public string OneFuzzNodeDisposalStrategy => throw new System.NotImplementedException();
-
     public ResourceIdentifier? OneFuzzDataStorage => throw new NotImplementedException();
 
     public string? OneFuzzResourceGroup => throw new NotImplementedException();