UI: Update <a> tags to LinkTo's (#17866)

* chore: shared external link component, glimmerization

* chore: update easy a tags

* chore: update other a tags

* chore: lil cleanup

* changelog

ui/lib/core/addon/components/learn-link.js

@@ -1,5 +1,22 @@
-import DocLink from './doc-link';
+import ExternalLink from './external-link';
 
-export default DocLink.extend({
-  host: 'https://learn.hashicorp.com',
-});
+/**
+ * @module LearnLink
+ * `LearnLink` components are used to render anchor links to relevant Vault learn documentation at learn.hashicorp.com.
+ *
+ * @example
+ * ```js
+    <LearnLink @path="/docs/secrets/kv/kv-v2.html">Learn about KV v2</LearnLink>
+ * ```
+ *
+ * @param path="/"{String} - The path to documentation on learn.hashicorp.com that the component should link to.
+ *
+ */
+
+export default class LearnLinkComponent extends ExternalLink {
+  host = 'https://learn.hashicorp.com';
+
+  get href() {
+    return `${this.host}${this.args.path}`;
+  }
+}