Edit branch rules: BE/FE integration for deploy keys

Use prepared endpoint for searching for deploy keys, when setting branch protection.

• issue introducing GraphQL query: #432494 (closed)
• component that should consume the query: https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/assets/javascripts/vue_shared/components/list_selector/index.vue?ref_type=heads#L199
• missing unit tests: https://gitlab.com/gitlab-org/gitlab/-/blob/master/spec/frontend/vue_shared/components/list_selector/index_spec.js?ref_type=heads#L390

As a result, the user should be able to search through and select deploy keys inside the drawer for Allowed to merge and Allowed to push ad merge sections on Branch rule details page: