Provide aggregated documentation for offline use

Hi,

Seems that with Spring Boot 3.3.0 you have removed the single page variant of the reference documentation, as it now redirects to https://docs.spring.io/spring-boot/index.html. Please restore it, it's necessary for

1. fast cross referencing across the entire framework and
2. finding things which one can't remember exact names/keywords for

The segmented reference at https://docs.spring.io/spring-boot/index.html is useful only if one already knows the general structure of the whole documentation, which really doesn't apply to a casual reader since Boot is a massive project.

Start by reviewing the segmented reference documentation at https://docs.spring.io/spring-boot/index.html and the redirect behavior described in the issue. Determine how the former single-page reference was generated or published, then verify that the complete Spring Boot reference can be accessed as one document for offline searching and cross-referencing.