Add convertToDraft for pull requests

fixes #2197

Author: mawinter69

src/main/java/org/kohsuke/github/GHPullRequest.java

@@ -160,6 +160,30 @@ public boolean canMaintainerModify() throws IOException {
         return maintainerCanModify;
     }
 
+    /**
+     * Converts a pull request from ready for review to draft
+     *
+     * @throws IOException
+     *             the io exception
+     * @throws IllegalStateException
+     *             if the pull request is not a draft
+     */
+    public void convertToDraft() throws IOException {
+        if (draft) {
+            throw new IllegalStateException("Pull request is already a draft");
+        }
+
+        StringBuilder inputBuilder = new StringBuilder();
+        addParameter(inputBuilder, "pullRequestId", this.getNodeId());
+
+        String graphqlBody = "mutation ConvertToDraft { convertPullRequestToDraft(input: {" + inputBuilder
+                + "}) { pullRequest { id } } }";
+
+        root().createGraphQLRequest(graphqlBody).sendGraphQL();
+
+        refresh();
+    }
+
     /**
      * Create review gh pull request review builder.
      *
@@ -275,6 +299,10 @@ public GHCommitPointer getBase() {
         return base;
     }
 
+    //
+    // details that are only available via get with ID
+    //
+
     /**
      * Gets changed files.
      *
@@ -287,10 +315,6 @@ public int getChangedFiles() throws IOException {
         return changedFiles;
     }
 
-    //
-    // details that are only available via get with ID
-    //
-
     /**
      * Gets the closed by.
      *

src/test/java/org/kohsuke/github/GHPullRequestTest.java

@@ -225,6 +225,49 @@ public void commentsInPullRequestReviewBuilder() {
         assertThat(multilineDraftReviewComment.getLine(), equalTo(2));
     }
 
+    /**
+     * Test marking a draft pull request as ready for review.
+     *
+     * @throws Exception
+     *             the exception
+     */
+    @Test
+    public void convertToDraft() throws Exception {
+        // Create a draft PR first
+        GHPullRequest p = getRepository()
+                .createPullRequest("convertToDraft", "test/stable", "main", "## test", false, false);
+        assertThat(p.isDraft(), is(false));
+
+        // Mark it ready for review
+        p.convertToDraft();
+
+        // Verify it's no longer a draft
+        assertThat(p.isDraft(), is(true));
+    }
+
+    /**
+     * Test marking a draft pull request as ready for review.
+     *
+     * @throws Exception
+     *             the exception
+     */
+    @Test
+    public void convertToDraftFromDraft() throws Exception {
+        // Create a draft PR first
+        GHPullRequest p = getRepository()
+                .createPullRequest("convertToDraft", "test/stable", "main", "## test", false, true);
+        assertThat(p.isDraft(), is(true));
+
+        // Mark it ready for review
+        try {
+            p.convertToDraft();
+            fail("Expected IllegalStateException");
+        } catch (IllegalStateException e) {
+            assertThat(e.getMessage(), equalTo("Pull request is already a draft"));
+        }
+
+    }
+
     /**
      * Creates the draft pull request.
      *