Fix usage of docs-release templating

[izgeri]

Summary

Currently when we use html templates, they are not using html/template package but text/template and thus not loading the partials either.

Steps to Reproduce

• Run ./parse-changelogs -t docs-release

Expected Results

All output should follow html/template pattern where needed

Actual Results (including error logs, if applicable)

Output uses plain text/template transformation

Acceptance Criteria

• Ensure html templates use the proper template package
• Ensure html partials can work in integration test(s)
• Ensure that (if merged at that time) installation instructions for Conjur are moved to a partial