refactor: Render booking pages in operator context

[MoritzWeber0]

This is a huge one. It completely changes the rendering logic of booking pages. Instead of displaying the rendered version of the booking page on the operator page, we do now render it on demand in the operator page context. With some additional changes in this PR, this will fix many issues:

• Irrelevant sections of booking expanders are no longer rendered to the DOM. This fixes an issue where results where displayed in the search, but were not available on the page itself (see issue description below)
• Images can be rendered out of context now. If you want to render the an image in another page context (for example to render a booking image on an operator page), just write:

  ![DB reservation booking](db_reservation.de.webp)
  {page="booking/db-website"}
  

• Footnotes of booking expanders are finally scoped globally and are no longer rendered locally inside the expander
• The heading map does now properly handle expanders, can be checked via the HeadingsMap extension
• Content of the following expander doesn't count as element from the previous expander in the search (as there was no heading in between, so it counted as element of the last heading of the previous expander)
• Train categories and booking platforms title matches are ranked higher in the search
• If the result targets a booking or train category expander, the page automatically scrolls to it.
• Similar to the already existing behavior with train category expanders, it's now possible to link to booking platforms directly, e. g. https://deploy-preview-856--fipguide.netlify.app/de/operator/oebb/#oebb-website works now.

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Issue description

So far, we only hide some booking sections using display: none in the CSS of booking expanders. The issue is: Even if hidden, the content is still indexed for the search.

This PR changes the approach to no longer render the irrelevant sections to the DOM by storing the rendered sections in the page store.

Steps to reproduce the search issue:

1. Search for "Website der Deutschen Bahn" on the German page
2. Select "Reservierungen":
   
3. The section doesn't exist, no scrolling happens

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Resolves #887
Resolves #462

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[github-actions]

Hi there! 👋

Thank you for your contribution to the FIP Guide! 🚀
We appreciate your effort in making rail staff travel information more accessible. 🚄

Checklist before merging:

• Added a description to the Pull Request
• Checked the License of new pictures (non-commercial use without attribution)
• Modified content in English
• Modified content in German
• Modified content in French