Scroll to the top of reader content when primary navigation link is clicked

When navigating between pages using the primary sidebar navigation menu,
scroll to the top of the generated markdown content via
`.scrollIntoView()`.

Signed-off-by: Colton Padden <colton.padden@fastmail.com>

.changeset/dull-news-visit.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-techdocs': patch
+---
+
+Reader will now scroll to the top of the page when navigating between pages

plugins/techdocs/src/reader/components/Reader.tsx

@@ -321,6 +321,7 @@ export const useTechDocsReaderDom = (): Element | null => {
           baseUrl: window.location.origin,
           onClick: (_: MouseEvent, url: string) => {
             const parsedUrl = new URL(url);
+            // hash exists when anchor is clicked on secondary sidebar
             if (parsedUrl.hash) {
               navigate(`${parsedUrl.pathname}${parsedUrl.hash}`);
               // Scroll to hash if it's on the current page
@@ -329,6 +330,10 @@ export const useTechDocsReaderDom = (): Element | null => {
                 ?.scrollIntoView();
             } else {
               navigate(parsedUrl.pathname);
+              // Scroll to top of reader if primary sidebar link is clicked
+              transformedElement
+                ?.querySelector('.md-content__inner')
+                ?.scrollIntoView();
             }
           },
         }),