Add copy button to code blocks (#16052)

* Add deps

* Setup copy events

* Updoot

* Tweak styling

* Do a lil' proof-of-concept

* Updoot @github-docs/render-content

* Use SCSS variables for custom styles

* Adjust docs

* Ignore clipboard in check-deps

* Add copy annotation to quickstart workflow sample

Co-authored-by: Cynthia Rich <crichID@users.noreply.github.com>

javascripts/copy-code.js

@@ -0,0 +1,15 @@
+import Clipboard from 'clipboard'
+
+export default () => {
+  const clipboard = new Clipboard('button.js-btn-copy')
+
+  clipboard.on('success', evt => {
+    const btn = evt.trigger
+    const beforeTooltip = btn.getAttribute('aria-label')
+    btn.setAttribute('aria-label', 'Copied!')
+
+    setTimeout(() => {
+      btn.setAttribute('aria-label', beforeTooltip)
+    }, 2000)
+  })
+}