added page for custom steps

Author: haleychaas

docs/content/guides/custom-steps

@@ -0,0 +1,76 @@
+---
+title: Custom Steps
+lang: en
+---
+
+Your app can use the `function()` method to listen to incoming [custom step requests](https://docs.slack.dev/workflows/workflow-steps). Custom steps are used in Workflow Builder to build workflows. The method requires a step `callback_id` of type string. This `callback_id` must also be defined in your [Function](https://docs.slack.dev/reference/app-manifest#functions) definition. Custom steps must be finalized using the `complete()` or `fail()` listener arguments to notify Slack that your app has processed the request.
+
+* `complete()` requires one argument: an `outputs` object. It ends your custom step successfully and provides an object containing the outputs of your custom step as per its definition.
+* `fail()` requires one argument: `error` of type `string`. It ends your custom step unsuccessfully and provides a message containing information regarding why your custom step failed.
+
+You can reference your custom step's inputs using the `getInputs()` method shown below.
+
+```java
+app.function("sample_function", (req, ctx) -> {
+  app.executorService().submit(() -> {
+    try {
+      var userId = req.getEvent().getInputs().get("user_id").asString();
+      var response = ctx.client().chatPostMessage(r -> r
+        .channel(userId) // sending a DM
+        .text("Hi! Thank you for submitting the request! We'll let you know once the processing completes.")
+      );
+      var outputs = new HashMap<String, Object>();
+      outputs.put("channel_id", response.getChannel());
+      outputs.put("ts", response.getTs());
+      ctx.complete(outputs);
+    } catch (Exception e) {
+      ctx.logger.error(e.getMessage(), e);
+      try {
+        ctx.fail("Failed to handle 'sample_function' custom step execution (error: " + e.getMessage() + ")");
+      } catch (Exception ex) {
+        ctx.logger.error(e.getMessage(), e);
+      }
+    }
+  });
+  return ctx.ack();
+});
+```
+
+The corresponding app manifest function definition for the preceding function might look like this:
+
+```json
+"functions": {
+    "sample_function": {
+        "title": "Send a request",
+        "description": "Send some request to the backend",
+        "input_parameters": {
+            "user_id": {
+                "type": "slack#/types/user_id",
+                "title": "User",
+                "description": "Who to send it",
+                "is_required": true,
+                "hint": "Select a user in the workspace",
+                "name": "user_id"
+            }
+        },
+        "output_parameters": {
+            "channel_id": {
+                "type": "slack#/types/channel_id",
+                "title": "DM ID",
+                "description": "The DM ID",
+                "is_required": true,
+                "name": "channel_id"
+            },
+            "ts": {
+                "type": "string",
+                "title": "Message timestamp",
+                "description": "Sent message timestamp",
+                "is_required": true,
+                "name": "ts"
+            }
+        }
+    }
+}
+```
+
+Once your custom step is defined in your app's manifest and implemented in code, it is discoverable in Workflow Builder when you **Add Step** and search for the name of your app.

docs/sidebars.js

@@ -36,6 +36,7 @@ const sidebars = {
 					items: ['guides/interactive-components', 'guides/modals', 'guides/app-home',],
 				},  
         'guides/ai-apps',
+        'guides/custom-steps',
         'guides/shortcuts',
         'guides/slash-commands',
         {