refactor: use enum types for setPermission and setNotificationSetting

Addresses review feedback from @rozza-sb on #2219:

- setNotificationSetting now takes a new GHTeam.NotificationSetting
  enum (NOTIFICATIONS_ENABLED / NOTIFICATIONS_DISABLED) instead of a
  raw String. The enum overrides toString() to return the exact API
  values and is passed to .with("notification_setting", ...) as a
  String so transformEnum() doesn't rewrite the underscores.
- setPermission now takes GHOrganization.Permission (ADMIN, MAINTAIN,
  PULL, PUSH, TRIAGE) so callers can only pass valid values. The enum
  names lowercase cleanly into the API values the Teams endpoint
  expects, and reuses the enum that already exists in this package
  instead of inventing a new team-scoped one.

Author: mvanhorn

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

@@ -34,6 +34,28 @@ public enum Privacy {
         UNKNOWN
     }
 
+    /**
+     * Notification setting for a team. Controls whether members receive notifications when the team is mentioned.
+     */
+    public enum NotificationSetting {
+
+        /** Notifications enabled: members receive notifications when the team is @mentioned. */
+        NOTIFICATIONS_ENABLED("notifications_enabled"),
+        /** Notifications disabled: mentions of the team do not generate notifications. */
+        NOTIFICATIONS_DISABLED("notifications_disabled");
+
+        private final String apiValue;
+
+        NotificationSetting(String apiValue) {
+            this.apiValue = apiValue;
+        }
+
+        @Override
+        public String toString() {
+            return apiValue;
+        }
+    }
+
     /**
      * Member's role in a team.
      */
@@ -527,14 +549,14 @@ public void setName(String name) throws IOException {
      * Sets the team's notification setting.
      *
      * @param notificationSetting
-     *            the notification setting (e.g. "notifications_enabled" or "notifications_disabled")
+     *            the notification setting
      * @throws IOException
      *             the io exception
      */
-    public void setNotificationSetting(String notificationSetting) throws IOException {
+    public void setNotificationSetting(NotificationSetting notificationSetting) throws IOException {
         root().createRequest()
                 .method("PATCH")
-                .with("notification_setting", notificationSetting)
+                .with("notification_setting", notificationSetting.toString())
                 .withUrlPath(api(""))
                 .send();
     }
@@ -543,11 +565,11 @@ public void setNotificationSetting(String notificationSetting) throws IOExceptio
      * Sets the team's permission.
      *
      * @param permission
-     *            the permission (e.g. "pull", "push", or "admin")
+     *            the permission
      * @throws IOException
      *             the io exception
      */
-    public void setPermission(String permission) throws IOException {
+    public void setPermission(GHOrganization.Permission permission) throws IOException {
         root().createRequest().method("PATCH").with("permission", permission).withUrlPath(api("")).send();
     }