Feature request for cmake search alias

Currently theres no way to filter search to contain only cmake-related pages via search bar, or search URL. I suggest the word `cmake` and the alias `cm`.

Start by tracing how the search bar and search URL apply documentation filters, then find the existing alias definitions for other technologies. Add support for both `cmake` and `cm` as filters, and verify that each searches only CMake-related pages in the bar and URL.

Written by the indexing model from the issue text.