Show whether a PR is WIP inside popups (#28975)

Fixes https://codeberg.org/forgejo/forgejo/issues/2257

Draft status of a PR is currently not exposed by the API. This PR adds a
'draft' field to pull requests in the API, which is used to correctly
set the PR color/icon in a ContextPopup.

---

Before:

![image](https://github.com/go-gitea/gitea/assets/5541521/72cbd30e-1175-4338-aa97-ac99c46c5118)

After:

![image](https://github.com/go-gitea/gitea/assets/5541521/111c9eba-460e-4d57-bcca-23a151c3a4f1)

templates/swagger/v1_json.tmpl

@@ -21610,6 +21610,10 @@
       "description": "PullRequestMeta PR info if an issue is a PR",
       "type": "object",
       "properties": {
+        "draft": {
+          "type": "boolean",
+          "x-go-name": "IsWorkInProgress"
+        },
         "merged": {
           "type": "boolean",
           "x-go-name": "HasMerged"