Remove usage of deprecated modal-ok and modal-cancel slots

What does this MR do and why?

This addresses gitlab-ui#1471 (moved) and removes all usage of the modal-ok and modal-cancel slots, which have been deprecated since gitlab-ui!767 (merged).

Screenshots or screen recordings

app/assets/javascripts/packages_and_registries/infrastructure_registry/list/components/packages_list.vue

Before	After
infra_before	infra_after

app/assets/javascripts/packages_and_registries/package_registry/components/list/packages_list.vue

Before	After
packages_before	packages_after

ee/app/assets/javascripts/vue_merge_request_widget/components/approvals/approvals_auth.vue

Before	After
approval_before	approval_after

app/assets/javascripts/monitoring/components/duplicate_dashboard_modal.vue

🔶 Requires an k8s cluster for local env to create & duplicate dashboards, AFAIU. I need maintainer help to review this.

How to set up and validate locally

Package Registry:

• Create a new empty project.
• In your rails console: Project.last.packages.create(name: "gemgemgem", version: "1.2.3", package_type: "rubygems")

Infra Registry:

• In your rails console: Project.last.packages.create(name: "terra/foo", version: "0.0.1", package_type: "terraform_module")

EE Approval Auth:

• Activate an EE license key if you haven't yet.
• Go to any project that has open MRs and where you are Admin.
• In the project settings, enable "General / Merge request approvals / Require user password to approve".
• Go to any open MR and click approve.

Monitoring Dashboard Duplication:

I was not able to verify this change. Needs maintainer review help! 👈

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.