Add delimiter for ECS Changelog summary

[sravankumar985]

Summary

The Template Changelog summary is not delimited properly.

Ref: https://www.thethingsindustries.com/docs/enterprise/aws/ecs/

Screenshots

Before:

After:

Changes

Added a delimiter for the template changelog summary.

Notes for Reviewers

None.

Checklist

• Scope: The referenced issue is addressed, there are no unrelated changes.
• Run Locally: Verified that the docs build using make server, posted screenshots, verified external links. Test with HUGO_PARAMS_SEARCH_ENABLED=true if style changes will affect the search bar.
• New Features Marked: Documentation for new features is marked using the new-in-version shortcode, according to the guidelines in CONTRIBUTING.
• Style Guidelines: Documentation obeys style guidelines in CONTRIBUTING.
• Commits: Commit messages follow guidelines in CONTRIBUTING, there are no fixup commits left.

[KrishnaIyer]

This actually won't work as this entire file gets replaced every time a new release action is run.
This change should be here https://github.com/TheThingsIndustries/lorawan-stack/blob/v3.34/.github/workflows/generate-docs-pr.yml#L87-L93 @happyRip