Add authorAssociation field and getter to GHIssue

Deserialize the `author_association` field from the GitHub REST API on
issues and pull requests. Uses the same String-field + EnumUtils pattern
as GHIssueComment for forward-compatible enum parsing.

Author: Haarolean

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

@@ -121,6 +121,9 @@ protected static List<String> getLogins(Collection<GHUser> users) {
     /** The assignees. */
     protected GHUser[] assignees;
 
+    /** The author's association with the repository. */
+    protected String authorAssociation;
+
     /** The body. */
     @SkipFromToString
     protected String body;
@@ -349,6 +352,17 @@ public List<GHUser> getAssignees() {
         return Collections.unmodifiableList(Arrays.asList(assignees));
     }
 
+    /**
+     * Gets the author's association with the repository.
+     *
+     * @return the author association
+     */
+    public GHCommentAuthorAssociation getAuthorAssociation() {
+        return EnumUtils.getEnumOrDefault(GHCommentAuthorAssociation.class,
+                authorAssociation,
+                GHCommentAuthorAssociation.UNKNOWN);
+    }
+
     /**
      * The description of this pull request.
      *

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

@@ -169,6 +169,7 @@ public void createIssue() throws Exception {
         GHRepository repo = getRepository();
         GHIssue issue = repo.createIssue(name).body("## test").create();
         assertThat(issue.getTitle(), equalTo(name));
+        assertThat(issue.getAuthorAssociation(), equalTo(GHCommentAuthorAssociation.NONE));
     }
 
     /**