Add method to trigger housekeeping via the API. (#434)

Author: Schoaf

src/main/java/org/gitlab4j/api/ProjectApi.java

@@ -2931,4 +2931,19 @@ public void denyAccessRequest(Object projectIdOrPath, Integer userId) throws Git
         delete(Response.Status.NO_CONTENT, null,
                 "projects", getProjectIdOrPath(projectIdOrPath), "access_requests", userId);
     }
+
+  /**
+   * Start the Housekeeping task for a project.
+   *
+   * <pre>
+   * <code>GitLab Endpoint: POST /projects/:id/housekeeping</code>
+   * </pre>
+   *
+   * @param projectIdOrPath the project in the form of an Integer(ID), String(path), or Project instance
+   * @throws GitLabApiException if any exception occurs
+   */
+  public void triggerHousekeeping(Object projectIdOrPath) throws GitLabApiException {
+    Form formData = null;
+    post(Response.Status.OK, formData, "projects", getProjectIdOrPath(projectIdOrPath), "housekeeping");
+  }
 }