Merge branch 'bastirehm-internal-analytics-fundamental-docs' into 'master'

Add internal analytics fundamentals docs to index page

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/133446



Merged-by: Suzanne Selhorn <sselhorn@gitlab.com>
Approved-by: Jonas Larsen <jlarsen@gitlab.com>
Approved-by: Michał Wielich <mwielich@gitlab.com>
Reviewed-by: Michał Wielich <mwielich@gitlab.com>
Reviewed-by: Jonas Larsen <jlarsen@gitlab.com>
Co-authored-by: Michał Wielich <mwielich@gitlab.com>
Co-authored-by: Sebastian Rehm <srehm@gitlab.com>