api_docs: Add "event_types" common component.

To facilitate re-use of the same parameters in other paths. this commit
store the content of the parameter "event_types" in components.

zerver/openapi/zulip.yaml

@@ -2346,23 +2346,7 @@ paths:
           type: boolean
           default: false
         example: true
-      - name: event_types
-        in: query
-        description: "A JSON-encoded array indicating which types of events
-          you're interested in. Values that you might find useful include:
-          <br/> <br/>
-          * **message** (messages), <br/>
-          * **subscription** (changes in your subscriptions), <br/>
-          * **realm_user** (changes in the list of users in your realm)
-          <br/> <br/>
-          If you do not specify this argument, you will receive all events,
-          and have to filter out the events not relevant to your client in
-          your client code. For most applications, one is only interested in
-          messages, so one specifies: `event_types=['message']`"
-        schema:
-          type: array
-          items:
-            type: string
+      - $ref: '#/components/parameters/Event_types'
         example: ['message']
       - name: all_public_streams
         in: query
@@ -3240,30 +3224,8 @@ paths:
             type: string
         example: narrow=['stream', 'Denmark']
         required: false
-      - name: event_types
-        in: query
-        description: |
-          A JSON-encoded array indicating which types of events you're
-          interested in. Values that you might find useful include:
-
-            * **message** (messages)
-            * **subscription** (changes in your subscriptions)
-            * **realm_user** (changes to users in the organization and
-              their properties, such as their name).
-
-          If you do not specify this argument, you will receive all
-          events, and have to filter out the events not relevant to
-          your client in your client code.  For most applications, one
-          is only interested in messages, so one specifies:
-          `event_types=['message']`
-        schema:
-          type: array
-          items:
-            type: string
-          default:
+      - $ref: '#/components/parameters/Event_types'
         example: event_types=['message']
-        required: false
-        default: null
       security:
       - basicAuth: []
   /rest-error-handling:
@@ -3539,3 +3501,32 @@ components:
         application/json:
           schema:
             $ref: '#/components/schemas/JsonSuccess'
+
+  ####################
+  # Shared parameters
+  ####################
+  parameters:
+    Event_types:
+      name: event_types
+      in: query
+      description: |
+        A JSON-encoded array indicating which types of events you're
+        interested in. Values that you might find useful include:
+
+          * **message** (messages)
+          * **subscription** (changes in your subscriptions)
+          * **realm_user** (changes to users in the organization and
+            their properties, such as their name).
+
+        If you do not specify this argument, you will receive all
+        events, and have to filter out the events not relevant to
+        your client in your client code.  For most applications, one
+        is only interested in messages, so one specifies:
+        `event_types=['message']`
+      schema:
+        type: array
+        items:
+          type: string
+        default:
+      required: false
+      default: null