Add API to get merged PR of a commit (#29243)

Adds a new API `/repos/{owner}/{repo}/commits/{sha}/pull` that allows
you to get the merged PR associated to a commit.

---------

Co-authored-by: 6543 <6543@obermui.de>

templates/swagger/v1_json.tmpl

@@ -4565,6 +4565,49 @@
         }
       }
     },
+    "/repos/{owner}/{repo}/commits/{sha}/pull": {
+      "get": {
+        "produces": [
+          "application/json"
+        ],
+        "tags": [
+          "repository"
+        ],
+        "summary": "Get the pull request of the commit",
+        "operationId": "repoGetCommitPullRequest",
+        "parameters": [
+          {
+            "type": "string",
+            "description": "owner of the repo",
+            "name": "owner",
+            "in": "path",
+            "required": true
+          },
+          {
+            "type": "string",
+            "description": "name of the repo",
+            "name": "repo",
+            "in": "path",
+            "required": true
+          },
+          {
+            "type": "string",
+            "description": "SHA of the commit to get",
+            "name": "sha",
+            "in": "path",
+            "required": true
+          }
+        ],
+        "responses": {
+          "200": {
+            "$ref": "#/responses/PullRequest"
+          },
+          "404": {
+            "$ref": "#/responses/notFound"
+          }
+        }
+      }
+    },
     "/repos/{owner}/{repo}/contents": {
       "get": {
         "produces": [