Add API to manipulate "glowing" state of an Entity.

When an Entity is "glowing" they will have an outline around them as if they have been hit by a Spectral Arrow.

By: md_5 <git@md-5.net>

paper-api/src/main/java/org/bukkit/entity/Entity.java

@@ -342,4 +342,18 @@ public interface Entity extends Metadatable, CommandSender {
      * @return if the custom name is displayed
      */
     public boolean isCustomNameVisible();
+
+    /**
+     * Sets whether the entity has a team colored (default: white) glow.
+     *
+     * @param flag if the entity is glowing
+     */
+    void setGlowing(boolean flag);
+
+    /**
+     * Gets whether the entity is glowing or not.
+     *
+     * @return whether the entity is glowing
+     */
+    boolean isGlowing();
 }