[Docs] Remove hosting topics already covered by shipped configs

[mcop1]

Part of pimcore/product-management#1149, as suggested in https://github.com/pimcore/product-management/issues/1149#issuecomment-4863189462.

What's changed

• Removed the System Setup and Hosting pages that are already covered by the pre-configured Docker environment shipped with the installation packages and the official Pimcore Docker images:
  • Apache Configuration
  • Nginx Configuration
  • File Permissions
  • Database Setup
  • Additional Tools Installation
• Moved the Gotenberg/LibreOffice setup details (only documented on the removed Additional Tools page) into the Office Document Preview section of Advanced Installation Topics.
• Updated dangling references: the Nginx sample config now points to the skeleton .docker/nginx.conf, and System Requirements now notes that the additional server tools are pre-installed in the official Docker images.
• Kept the numbering of the remaining pages (04/06/08/09) since the Performance Guide is deep-linked by filename from the pimcore/pimcore docs.

Related PRs

• Add optional thumbnail generation overload protection to nginx.conf skeleton#276 — moves the Thumbnail Generation Overload Protection reference config into the skeleton nginx.conf
• [Docs] Fix links to removed System Setup and Hosting pages pimcore#19238 — fixes core doc links pointing to the removed pages

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