mark deprecated AppID components for removal

The AppID backend is no longer available in the latest Vault releases,
so we plan removal with a following major release.

src/test/java/de/stklcode/jvault/connector/model/AuthBackendTest.java

@@ -33,6 +33,7 @@ class AuthBackendTest {
      * Test forType() method.
      */
     @Test
+    @SuppressWarnings("deprecation")
     void forTypeTest() {
         assertEquals(AuthBackend.TOKEN, AuthBackend.forType("token"));
         assertEquals(AuthBackend.APPID, AuthBackend.forType("app-id"));