add: fetch gh branches

actions/github/repository.ts

@@ -46,3 +46,16 @@ export async function getUserRepository(userId: string, username: string): Promi
 
     return repositories.repositories as GithubRepository[];
 }
+
+export async function getRepositoryBranches(userId: string, username: string, repository: string): Promise<string[]> {
+    const branches = await fetch(`https://api.github.com/repos/${username}/${repository}/branches`, {
+        headers: {
+            Authorization: `Bearer ${await getInstallationAccessToken(userId, username)}`,
+            Accept: "application/vnd.github+json",
+            "X-GitHub-Api-Version": "2022-11-28",
+        },
+        method: 'GET',
+    }).then(res => res.json());
+
+    return branches.map((branch: { name: string }) => branch.name) as string[];
+}