No leading/trailing spaces when generating heading ids (Fixes #57528)

What does this MR do?

Fixes #57528 (closed)

This removes leading and trailing spaces from heading when generating id to anchor the heading in Markdown.

Before this MR, this code in a Markdown document

<h1>
  Title
</h1>

would be anchored via #-title.

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content