Adds a new documentation page for the incremental repair feature.
The page covers:
- What incremental repair is and its benefits over the standard repair process.
- How it works at a high level by tracking the repair status of SSTables.
- The prerequisite of using the tablets architecture.
- The different user-configurable modes: 'regular', 'full', and 'disabled'.
Fixes#25600Closesscylladb/scylladb#26221
3cf1225ae6