UI - make engine list more consistent with the auth method list (#4598)

* remove expanding behavior from engines list and add a configuration route

* use page header component, secret tab component for the template on the secret engine configuration route

* move abstraction to secret-list-header and remove secret-tabs

* add attrs to secret engine model and adjust mount controller code to support that

* fix top level nav so that we can use the back button properly

* fix tests

ui/tests/pages/secrets/backend/configuration.js

@@ -0,0 +1,7 @@
+import { create, visitable, text } from 'ember-cli-page-object';
+
+export default create({
+  visit: visitable('/vault/secrets/:backend/configuration'),
+  defaultTTL: text('[data-test-row-value="Default Lease TTL"]'),
+  maxTTL: text('[data-test-row-value="Max Lease TTL"]'),
+});