changes bottlerocket variant to ecs-2 and adds link to docs for updater

[stockholmux]

Description

• ecs-2 variant is a more current variant type
• Adds link to ECS Updater docs

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• [x] Understand the repository structure
• [x] Add yourself as an author
• [x] Add your pattern
• [x] Add a great SVG diagram for your pattern
• [x] Read our general contribution guidelines
• [x] Read our code of conduct
• [x] Confirm your pattern frontmatter lints correctly. i.e. run npm install && npm run lint locally from your dev environment