Allow pulumi.Output in EKS Addon configurationValues (#1632)

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### Proposed changes

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Someone went through the effort of creating a stringify function and
forgot to use it 😁

**Edit by @guineveresaenger:** To preserve ordering I took the author's
suggestion and used `pulumi.jsonStringify`. This should fix up the PR
enough to be mergeable. If a reviewer would like ordering-specific
testing, we can do so; however this is a minor enough refactor that I do
not think explicit test is warranted.

---------

Co-authored-by: guineveresaenger <guinevere@pulumi.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: 3 people

nodejs/eks/addons/addon.ts

@@ -24,7 +24,7 @@ import { Cluster } from "../cluster";
 export interface AddonOptions
     extends Omit<aws.eks.AddonArgs, "resolveConflicts" | "clusterName" | "configurationValues"> {
     cluster: Cluster;
-    configurationValues?: object;
+    configurationValues?: pulumi.Input<object>;
 }
 
 /**
@@ -37,17 +37,18 @@ export class Addon extends pulumi.ComponentResource {
     constructor(name: string, args: AddonOptions, opts?: pulumi.CustomResourceOptions) {
         const cluster = args.cluster;
 
-        super("eks:index:Addon", name, args, {
-            ...opts,
+        super("eks:index:Addon", name, args, pulumi.mergeOptions(opts, {
             parent: cluster,
-        });
+        }));
 
         const addon = new aws.eks.Addon(
             name,
             {
                 ...args,
                 clusterName: cluster.core.cluster.name,
-                configurationValues: JSON.stringify(args.configurationValues),
+                configurationValues: args.configurationValues
+                    ? pulumi.jsonStringify(args.configurationValues)
+                    : undefined,
             },
             { parent: this, provider: opts?.provider },
         );