add external selection

src/main/java/com/mattmalec/pterodactyl4j/application/entities/PteroApplication.java

@@ -552,6 +552,9 @@ default PteroAction<ApplicationServer> retrieveServerById(long id) {
 	 *
 	 * @return {@link com.mattmalec.pterodactyl4j.PteroAction PteroAction} - Type {@link java.util.List List} of {@link com.mattmalec.pterodactyl4j.application.entities.ApplicationServer ApplicationServers}
 	 */
+
+	PteroAction<ApplicationServer> retrieveServerByExternalId(String id);
+
 	PteroAction<List<ApplicationServer>> retrieveServersByName(String name, boolean caseSensitive);
 
 	/**

src/main/java/com/mattmalec/pterodactyl4j/application/entities/impl/PteroApplicationImpl.java

@@ -276,6 +276,15 @@ public PaginationAction<ApplicationServer> retrieveServers() {
 				api, Route.Servers.LIST_SERVERS.compile(), (object) -> new ApplicationServerImpl(this, object));
 	}
 
+	@Override
+	public PteroAction<ApplicationServer> retrieveServerByExternalId(String id) {
+		return PteroActionImpl.onRequestExecute(
+				api,
+				Route.Servers.GET_SERVER_EXTERNAL.compile(id),
+				(response, request) -> new ApplicationServerImpl(this, response.getObject())
+		);
+	}
+
 	@Override
 	public PteroAction<ApplicationServer> retrieveServerById(String id) {
 		return PteroActionImpl.onRequestExecute(

src/main/java/com/mattmalec/pterodactyl4j/requests/Route.java

@@ -73,6 +73,8 @@ public static class Servers {
 				GET,
 				APPLICATION_PREFIX
 						+ "servers/{server_id}?include=allocations,user,subusers,nest,egg,location,node,databases");
+		public static final Route GET_SERVER_EXTERNAL =
+				new Route(GET, APPLICATION_PREFIX + "servers/external/{external_id}" );
 		public static final Route UPDATE_SERVER_DETAILS =
 				new Route(PATCH, APPLICATION_PREFIX + "servers/{server_id}/details");
 		public static final Route UPDATE_SERVER_BUILD =