ux: add scroll position lock for default docs sidebar

// Adds scroll position lock for default docs sidebar

if (document.querySelector('#sidebar-default') !== null) {

  let sidebar = document.getElementById('sidebar-default');

  let pos = sessionStorage.getItem('sidebar-scroll');

  if (pos !== null) {

      sidebar.scrollTop = parseInt(pos, 10);

  }

  window.addEventListener('beforeunload', () => {

      sessionStorage.setItem('sidebar-scroll', sidebar.scrollTop);

  });

}

{{ define "main" }}

	<div class="row flex-xl-nowrap">

		<div class="col-lg-5 col-xl-4 docs-sidebar d-none d-lg-block">

			<nav class="docs-links" aria-label="Main navigation">

			<nav {{ if eq .Site.Params.menu.section.collapsibleSidebar false }}id="sidebar-default" {{ end }}class="docs-links" aria-label="Main navigation">

				{{ partial "sidebar/docs-menu.html" . }}

			</nav>

		</div>