Add new layout for trial sign up

New layout includes new header with ui-indigo theme
and Tanuki logo in the center.

ee/app/assets/stylesheets/pages/trial.scss

+.trial-page {
+  @extend .login-page;
+}

ee/app/views/layouts/header/_logo_with_title.html.haml

+%header.navbar.fixed-top.navbar-gitlab.justify-content-center
+  = render 'shared/logo.svg'
+  %span.logo-text.d-none.d-lg-block.prepend-left-8.pt-1
+    = render 'shared/logo_type.svg'

ee/app/views/layouts/trial.html.haml

+!!! 5
+%html{ lang: "en" }
+  = render "layouts/head"
+  %body.ui-indigo.trial-page.application.navless
+    = render "layouts/header/logo_with_title"
+    = render "layouts/broadcast"
+    .container.navless-container
+      .content
+        = render "layouts/flash"
+        = yield

ee/changelogs/unreleased/vslobodin-trial-layout-impl.yml

+---
+title: Add new layout for trial
+merge_request: 15630
+author:
+type: added