[Dashboard] Add timeout to block() for HTTP requests to Github (#1751)

There was an incident at Github on Sep 22 that caused one of the HTTP
requests we sent to Github never returned and thus blocked the entire
sync process.

No idea why the underlying HTTP client library didn't throw an error in
this case, but we should add a timeout to the `block()` anyway.

Fixes #1732.

Author: coeuvre

dashboard/server/src/main/java/build/bazel/dashboard/common/RestApiClient.java

@@ -2,6 +2,7 @@
 
 import com.google.common.base.Strings;
 import java.net.URI;
+import java.time.Duration;
 import java.util.function.Function;
 import javax.annotation.Nullable;
 import lombok.extern.slf4j.Slf4j;
@@ -37,7 +38,7 @@ protected RestApiResponse exchange(WebClient.RequestHeadersSpec<?> spec) {
     return spec.exchangeToMono(response -> {
       log.debug("{} {}", response.statusCode(), response.headers().asHttpHeaders().toSingleValueMap());
       return RestApiResponse.fromClientResponse(response);
-    }).block();
+    }).block(Duration.ofSeconds(120));
   }
 
 }