Replace prepend-top-20 css class

Summary

As part of our efforts to move to gitlab-ui based utility classes in #217418

We should move the prepend-top-20 class to the gitlab-ui utility class of gl-mt-5 or gl-mt-6 depending on the design

The file list that contain the aforementioned class is listed below

File	converted
app/views/doorkeeper/applications/index.html.haml
app/views/devise/unlocks/new.html.haml	✅
app/views/devise/passwords/edit.html.haml	✅
app/views/devise/passwords/new.html.haml	✅
app/views/devise/sessions/two_factor.html.haml	✅
app/views/devise/confirmations/almost_there.haml	✅
app/views/devise/confirmations/new.html.haml	✅
app/views/ci/variables/_index.html.haml	✅
app/views/projects/no_repo.html.haml
app/views/projects/_archived_notice.html.haml
app/views/projects/compare/index.html.haml
app/views/clusters/clusters/gcp/_form.html.haml
app/views/shared/_import_form.html.haml
app/views/groups/dependency_proxies/_url.html.haml
app/views/groups/dependency_proxies/show.html.haml
app/views/groups/_archived_projects.html.haml
app/views/groups/_subgroups_and_projects.html.haml
app/views/groups/_shared_projects.html.haml
app/views/explore/groups/_groups.html.haml
app/views/dashboard/groups/_groups.html.haml
app/views/dashboard/_sidebar.html.haml
app/views/users/show.html.haml
app/views/users/calendar_activities.html.haml
app/assets/javascripts/commit/pipelines/pipelines_table.vue
app/assets/javascripts/snippets/components/show.vue
app/assets/javascripts/snippets/components/snippet_blob_edit.vue
app/assets/javascripts/snippets/components/edit.vue
app/assets/javascripts/pipelines/components/pipelines_list/pipelines.vue
app/assets/javascripts/groups/components/app.vue
app/assets/javascripts/frequent_items/components/app.vue
app/assets/javascripts/diffs/components/tree_list.vue
app/assets/javascripts/jobs/components/job_app.vue
app/assets/stylesheets/framework/common.scss
ee/app/views/projects/_marked_for_deletion_notice.haml
ee/app/views/projects/_new_ci_cd_only_project_pane.html.haml
ee/app/views/projects/_archived_notice.html.haml
ee/app/views/projects/merge_requests/_code_owner_approval_rules.html.haml
ee/app/views/projects/_ancestor_group_marked_for_deletion_notice.html.haml
ee/app/views/groups/_self_or_ancestor_marked_for_deletion_notice.html.haml
ee/app/assets/javascripts/group_member_contributions/components/app.vue
ee/app/assets/javascripts/add_gitlab_slack_application/components/add_gitlab_slack_application.vue
ee/app/assets/javascripts/geo_nodes/components/app.vue

Risks