fix: correct usage of custom heading IDs

[pepopowitz]

❗ This resolves a build error on main.

Description

Fixes a build error from usage of unescaped { in text. This wasn't a problem before #4799 merged, and I forgot to update that branch from main before I merged it, so I didn't find it until publish_stage was broken on main. 😅

Adjusts the links to follow the docusaurus guidance.

When should this change go live?

• This is a bug fix, security concern, or something that needs urgent release support. (add bug or support label)
• This is already available but undocumented and should be released within a week. (add available & undocumented label)
• This is on a specific schedule and the assignee will coordinate a release with the DevEx team. (create draft PR and/or add hold label)
• This is part of a scheduled alpha or minor. (add alpha or minor label)
• There is no urgency with this change (add low prio label)

PR Checklist

• My changes are for the next minor and are in /docs directory (aka /next/).
• My changes are for an already released minor and are in /versioned_docs directory.

• I added a DRI, team, or delegate as a reviewer for technical accuracy and grammar/style:
  • Engineering team review
  • Technical writer review via @camunda/tech-writers unless working with an embedded writer.

[github-actions]

👋 🤖 🤔 Hello, @pepopowitz! Did you make your changes in all the right places?

These files were changed only in docs/. You might want to duplicate these changes in versioned_docs/version-8.6/.

• docs/reference/announcements/870.md

You may have done this intentionally, but we wanted to point it out in case you didn't. You can read more about the versioning within our docs in our documentation guidelines.

[mesellings]

Approved in principle, good catch, but I think @wollefitz should approve 👍

[pepopowitz]

In the interest of fixing main, I auto-merged this. If there is more feedback, I'll address it in a new PR.