docs migration - Deploying to Heroku

Source: documentation/server/guides/deploying/heroku.md
Proposed disposition: Needs determination — Heroku eliminated its free tier in 2022 and its relevance to typical Swift server use cases has diminished. Consider deprecating this page and redirecting to the deployment.md overview rather than migrating it.
Reviewer: @swiftlang/server-workgroup

Checklist

• Determine disposition (suggested: Deprecate — Heroku free tier eliminated) and confirm redirect target
• If deprecating: add redirect_to: pointing to the new deployment overview article in the ServerGuides catalog
• If migrating (if Heroku remains relevant): translate Jekyll markdown to DocC markdown, verify all Heroku CLI steps are current, and add to ServerGuides.docc/Documentation.md
• Submit PR (redirect or content) to the appropriate repository

Read documentation/server/guides/deploying/heroku.md first, then confirm with the Server workgroup whether Heroku should be deprecated and identify the deployment.md overview target. Done means either adding the specified redirect_to entry or migrating the page to DocC markdown and adding it to ServerGuides.docc/Documentation.md, followed by a pull request to the appropriate repository.