Add Block Kit Builder preview link to Slack blocks description (#2120)

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Fixes OPS-3362


<img width="373" height="290" alt="image"
src="https://github.com/user-attachments/assets/1ad371a6-0860-4de6-821e-623939521187"
/>

Author: Roman Snapko

packages/blocks/slack/src/lib/common/utils.ts

@@ -269,7 +269,8 @@ export function dynamicBlockKitProperties(): any {
         const result: any = {
           blocks: Property.Json({
             displayName: 'Block Kit blocks',
-            description: 'See https://api.slack.com/block-kit for specs',
+            description:
+              'See https://api.slack.com/block-kit for specs. Visual preview available at https://app.slack.com/block-kit-builder',
             required: true,
             defaultValue: [
               {