[ADF-2930] general purpose "Empty Page" component (#3296)

* empty content component

* fix selector name

* style fixes

* cleanup code

* docs for empty content

* update docs

* update docs

* use typography for icon

* layout fixes for Login (ported from ACA)

lib/core/login/components/login.component.scss

@@ -6,6 +6,10 @@
     $foreground: map-get($theme, foreground);
     $text-color-primary: mat-color($foreground, text);
 
+    .adf-login {
+        @include flex-column;
+    }
+
     .adf-login-content {
         background-size: cover;
         background-position: center;