feat(libstore/s3-binary-cache-store): implement abortMultipartUpload()

Implement `abortMultipartUpload()` for cleaning up incomplete multipart
uploads on error:

- Constructs URL with `?uploadId=ID` query parameter
- Issues `DELETE` request to abort the multipart upload

src/libstore/s3-binary-cache-store.cc

@@ -26,6 +26,14 @@ public:
 
 private:
     ref<S3BinaryCacheStoreConfig> s3Config;
+
+    /**
+     * Abort a multipart upload
+     *
+     * @see
+     * https://docs.aws.amazon.com/AmazonS3/latest/API/API_AbortMultipartUpload.html#API_AbortMultipartUpload_RequestSyntax
+     */
+    void abortMultipartUpload(std::string_view key, std::string_view uploadId);
 };
 
 void S3BinaryCacheStore::upsertFile(
@@ -37,6 +45,19 @@ void S3BinaryCacheStore::upsertFile(
     HttpBinaryCacheStore::upsertFile(path, istream, mimeType, sizeHint);
 }
 
+void S3BinaryCacheStore::abortMultipartUpload(std::string_view key, std::string_view uploadId)
+{
+    auto req = makeRequest(key);
+    req.setupForS3();
+
+    auto url = req.uri.parsed();
+    url.query["uploadId"] = uploadId;
+    req.uri = VerbatimURL(url);
+    req.method = HttpMethod::DELETE;
+
+    getFileTransfer()->enqueueFileTransfer(req).get();
+}
+
 StringSet S3BinaryCacheStoreConfig::uriSchemes()
 {
     return {"s3"};