Draft: Refine merge request template "New Static Analysis Check"

Provide more guidance on steps to be done when upgrading gitlab-styles on dependent projects.

This MR brings back some points from https://gitlab.com/gitlab-org/gitlab/-/blob/master/.gitlab/merge_request_templates/New%20Static%20Analysis%20Check.md but rephrase it a bit to match the slightly different process when upgrading gitlab-styles on dependent projects.

Screenshots

https://gitlab.com/gitlab-org/gitlab-styles/-/blob/pl-doc-new-static-analysis-check-upgrade/.gitlab/merge_request_templates/New%20Static%20Analysis%20Check.md

See it in action: https://gitlab.com/gitlab-org/gitlab-styles/-/merge_requests/72#check-list