Merge branch 'docs/cells-infra' into 'master'

Blueprint for Cells Infrastructure

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/142931



Merged-by: Kamil Trzciński <ayufan@ayufan.eu>
Approved-by: John Skarbek <jskarbek@gitlab.com>
Approved-by: Andrew Newdigate <andrew@gitlab.com>
Approved-by: Alessio Caiazza <376774-nolith@users.noreply.gitlab.com>
Approved-by: Sam Wiskow <swiskow@gitlab.com>
Approved-by: Kamil Trzciński <ayufan@ayufan.eu>
Reviewed-by: Kamil Trzciński <ayufan@ayufan.eu>
Reviewed-by: Steve Xuereb <sxuereb@gitlab.com>
Reviewed-by: Alessio Caiazza <376774-nolith@users.noreply.gitlab.com>
Reviewed-by: John Skarbek <jskarbek@gitlab.com>
Reviewed-by: Craig Miskell <cmiskell@gitlab.com>
Reviewed-by: Steve Abrams <sabrams@gitlab.com>
Co-authored-by: Steve Xuereb <sxuereb@gitlab.com>