chore: Add download link to release notes automation (#1400)

Author: ellisong

.github/actions/docs-pr/index.js

@@ -54,6 +54,7 @@ for (const change of versionData.changes) {
 const frontMatter = {
   releaseDate,
   version: args.tag.substr(1),
+  downloadLink: "https://www.npmjs.com/package/@newrelic/browser-agent",
   features: [],
   bugs: [],
   security: []

.github/actions/docs-pr/templates/release-notes.handlebars

@@ -2,6 +2,7 @@
 subject: Browser agent
 releaseDate: "{{frontMatter.releaseDate}}"
 version: {{frontMatter.version}}
+downloadLink: {{frontMatter.downloadLink}}
 features: {{frontMatter.features}}
 bugs: {{frontMatter.bugs}}
 security: {{frontMatter.security}}