Update attributes to use md links

[karenzone]

Describe the bug

The text comes in OK, but the link remains in asciidoctor format.
IIRC, the {{ess-leading-short}}attribute has source tracking embedded in the link. That might be a factor.

Expected behavior

Link would render and resolve correctly.
Bonus points if we can keep our source tracking.

Steps to reproduce

1. Build the logstash.md doc set
2. Go to http://localhost:3000/connecting-to-cloud.html

Tooling

• docs-builder
• migration tooling
• I'm not sure

[bmorelli25]

Changed the title as this is happening because the value for the ess-leadin attr is hard-coded to an asciidoc link

  ess-leadin:   "You can run Elasticsearch on your own hardware or use our hosted Elasticsearch Service that is available on AWS, GCP, and Azure. https://cloud.elastic.co/registration{ess-utm-params}[Try the Elasticsearch Service for free]."