Affect triage/needs-rebase on Pull Requests with merge conflicts

This adds the `triage/needs-rebase` label (or removes it) on opened pull-requests, making it easier to find pull-requests that require a rebase to be merged

src/main/java/io/quarkus/bot/MarkPullRequestAsNeedsRebase.java

@@ -0,0 +1,27 @@
+package io.quarkus.bot;
+
+import io.quarkiverse.githubapp.event.Push;
+import io.quarkus.bot.util.Labels;
+import org.kohsuke.github.GHEventPayload;
+import org.kohsuke.github.GHIssueState;
+import org.kohsuke.github.GHPullRequest;
+import org.kohsuke.github.GHRepository;
+
+import java.io.IOException;
+
+public class MarkPullRequestAsNeedsRebase {
+
+    void maintainNeedsRebaseLabel(@Push GHEventPayload.Push pushRequestPayload) throws IOException {
+        GHRepository repository = pushRequestPayload.getRepository();
+        for (GHPullRequest pullRequest : repository.getPullRequests(GHIssueState.OPEN)) {
+            Boolean mergeable = pullRequest.getMergeable();
+            if (mergeable != null) {
+                if (mergeable) {
+                    pullRequest.removeLabels(Labels.TRIAGE_NEEDS_REBASE);
+                } else {
+                    pullRequest.addLabels(Labels.TRIAGE_NEEDS_REBASE);
+                }
+            }
+        }
+    }
+}

src/main/java/io/quarkus/bot/util/Labels.java

@@ -14,6 +14,7 @@ public class Labels {
     public static final String AREA_PREFIX = "area/";
     public static final String AREA_INFRA = "area/infra";
     public static final String TRIAGE_INVALID = "triage/invalid";
+    public static final String TRIAGE_NEEDS_REBASE = "triage/needs-rebase";
     public static final String TRIAGE_NEEDS_TRIAGE = "triage/needs-triage";
     public static final String TRIAGE_WAITING_FOR_CI = "triage/waiting-for-ci";
     public static final String TRIAGE_QE = "triage/qe?";