webhooks: Update payload testdata and type for Bitbucket Server push events (#63161)

The plugin did not actually support push events yet, so this was newly
added.
Not sure where the existing testdata came from, maybe the bitbucket
native webhooks that don't support global scope, but this event was
never handled right.
To make sure we actually support the payload returned from the plugin,
this PR adjusts the payload.

This payload was gathered by running the bitbucket server plugin,
configuring a webhook to point at a local ngrok, and then pushing to a
repo.
The payload then appears in the ngrok UI.

Works on SRC-387

Test plan:

CI passes with the new testdata, and with the updated event type.

cmd/frontend/internal/repos/webhooks/testdata/bitbucket-server-push.json

@@ -1,74 +1,67 @@
 {
-  "eventKey": "repo:refs_changed",
-  "date": "2022-12-21T14:49:22+0000",
-  "actor": {
-    "name": "milton",
-    "emailAddress": "dev@sourcegraph.com",
-    "id": 1,
-    "displayName": "milton woof",
+  "createdDate": 1717777064737,
+  "user": {
+    "name": "admin",
+    "emailAddress": "admin@example.com",
     "active": true,
-    "slug": "milton",
+    "displayName": "Administrator",
+    "id": 2,
+    "slug": "admin",
     "type": "NORMAL",
-    "links": {
-      "self": [
-        {
-          "href": "https://bitbucket.sgdev.org/users/milton"
-        }
-      ]
-    }
+    "links": { "self": [{ "href": "http://localhost:7990/users/admin" }] },
+    "avatarUrl": "https://secure.gravatar.com/avatar/e64c7d89f26bd1972efa854d13d7dd61.jpg?s\u003d64\u0026d\u003dmm"
   },
   "repository": {
-    "slug": "test-2020-06-01",
-    "id": 10092,
-    "name": "test-2020-06-01",
-    "hierarchyId": "f6bb9c710c413bb2c5f0",
+    "slug": "rep_1",
+    "id": 1,
+    "name": "rep_1",
+    "hierarchyId": "2bba4665b20d5005be17",
     "scmId": "git",
     "state": "AVAILABLE",
     "statusMessage": "Available",
     "forkable": true,
     "project": {
-      "key": "PRIVATE",
-      "id": 3,
-      "name": "Private",
+      "key": "PROJECT_1",
+      "id": 1,
+      "name": "Project 1",
+      "description": "Default configuration project #1",
       "public": false,
       "type": "NORMAL",
       "links": {
-        "self": [
-          {
-            "href": "https://bitbucket.sgdev.org/projects/PRIVATE"
-          }
-        ]
-      }
+        "self": [{ "href": "http://localhost:7990/projects/PROJECT_1" }]
+      },
+      "avatarUrl": "/projects/PROJECT_1/avatar.png?s\u003d64\u0026v\u003d1681176287106"
     },
     "public": false,
+    "archived": false,
     "links": {
       "clone": [
         {
-          "href": "ssh://git@bitbucket.sgdev.org:7999/private/test-2020-06-01.git",
-          "name": "ssh"
+          "href": "http://localhost:7990/scm/project_1/rep_1.git",
+          "name": "http"
         },
         {
-          "href": "https://bitbucket.sgdev.org/scm/private/test-2020-06-01.git",
-          "name": "http"
+          "href": "ssh://git@localhost:7999/project_1/rep_1.git",
+          "name": "ssh"
         }
       ],
       "self": [
         {
-          "href": "https://bitbucket.sgdev.org/projects/PRIVATE/repos/test-2020-06-01/browse"
+          "href": "http://localhost:7990/projects/PROJECT_1/repos/rep_1/browse"
         }
       ]
     }
   },
-  "changes": [
+  "refChanges": [
     {
       "ref": {
-        "id": "refs/heads/rs/test-branch",
-        "displayId": "rs/test-branch",
+        "id": "refs/heads/master",
+        "displayId": "master",
         "type": "BRANCH"
       },
-      "refId": "refs/heads/rs/test-branch",
-      "fromHash": "e6dcba6b52fd349279a38d9fa25db894467de609",
-      "toHash": "4cd5ee68a039032fe8a613879fd73b242592ea6a",
+      "refId": "refs/heads/master",
+      "fromHash": "e54a46d4e4ddb7bb370070aa8a9b68e0ed959e5b",
+      "toHash": "b14f55bd2b206c1128676131f9d66c56ec19e388",
       "type": "UPDATE"
     }
   ]

internal/extsvc/bitbucketserver/events.go

@@ -41,7 +41,30 @@ func ParseWebhookEvent(eventType string, payload []byte) (e any, err error) {
 type PingEvent struct{}
 
 type PushEvent struct {
-	Repository Repo `json:"repository"`
+	Repository  Repo        `json:"repository"`
+	CreatedDate int64       `json:"createdDate"`
+	Changes     []RefChange `json:"changes"`
+}
+
+type RefChange struct {
+	Ref RefChangeRef `json:"ref"`
+	// "refId": "refs/heads/master",
+	RefID string `json:"refId"`
+	// "fromHash": "e54a46d4e4ddb7bb370070aa8a9b68e0ed959e5b",
+	FromHash string `json:"fromHash"`
+	// "toHash": "b14f55bd2b206c1128676131f9d66c56ec19e388",
+	ToHash string `json:"toHash"`
+	// "type": "UPDATE"
+	Type string `json:"type"`
+}
+
+type RefChangeRef struct {
+	// "id": "refs/heads/master",
+	ID string `json:"id"`
+	// "displayId": "master",
+	DisplayID string `json:"displayId"`
+	// "type": "BRANCH"
+	Type string `json:"type"`
 }
 
 type PullRequestActivityEvent struct {