feat(ui): Added link-button to ui-libs. (TV-855)

Squashed commit of the following:

commit 1aab96d7f243c77adbd806196f76b931f4445976
Author: Erik Tiekstra <erik.tiekstra@arbetsformedlingen.se>
Date:   Thu Oct 28 11:38:05 2021 +0200

    Added digi-link component to ui lib

libs/ui/link-button/link-button.component.scss

@@ -0,0 +1,13 @@
+@import 'mixins/buttons';
+
+.ui-link-button {
+  &--primary {
+    @include msfa__button;
+  }
+  &--secondary {
+    @include msfa__button('secondary');
+  }
+  &--tertiary {
+    @include msfa__button('tertiary');
+  }
+}