hotspots: Add 'type' field to objects in 'hotspots' array.

This commit adds a 'type' field to the objects
in 'hotspots' array sent in 'hotspots' events.

We have explicitly added this field as we eventually
plan to have two type of onboarding steps, 'hotspots'
and 'one_time_notice'.

This will help clients to easily identify them.

zerver/lib/event_schema.py

@@ -334,6 +334,7 @@ def check_heartbeat(
 
 _hotspot = DictType(
     required_keys=[
+        ("type", str),
         ("name", str),
         ("title", str),
         ("description", str),

zerver/lib/hotspots.py

@@ -19,6 +19,7 @@ class Hotspot:
 
     def to_dict(self, delay: float = 0) -> Dict[str, Union[str, float, bool]]:
         return {
+            "type": "hotspot",
             "name": self.name,
             "title": str(self.title),
             "description": str(self.description),

zerver/openapi/zulip.yaml

@@ -2298,6 +2298,7 @@ paths:
                                   "hotspots":
                                     [
                                       {
+                                        "type": "hotspot",
                                         "name": "intro_streams",
                                         "title": "Catch up on a stream",
                                         "description": "Messages sent to a stream are seen by everyone subscribed to that stream. Try clicking on one of the stream links below.",
@@ -18557,10 +18558,11 @@ components:
       description: |
         Dictionary containing details of a single hotspot.
       properties:
-        delay:
-          type: number
+        type:
+          type: string
           description: |
-            The delay after which the user should be shown the hotspot.
+            The type of the onboarding step. Valid values are either
+            'hotspot' or 'one_time_notice'.
         name:
           type: string
           description: |
@@ -18574,6 +18576,10 @@ components:
           description: |
             The description of the hotspot, as will be displayed to the
             user.
+        delay:
+          type: number
+          description: |
+            The delay after which the user should be shown the hotspot.
         has_trigger:
           type: boolean
           description: |