Merge branch 'title-case-to-do-list' into 'master'

Use title case for To-Do List in docs and UI

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/173519



Merged-by: Suzanne Selhorn <sselhorn@gitlab.com>
Approved-by: Suzanne Selhorn <sselhorn@gitlab.com>
Co-authored-by: Ashraf Khamis <akhamis@gitlab.com>