Resolve duplication `project-feature-toggle` buttons

This is a follow up issue discussed in MR !15862 (comment 227661390)

Resolve the duplication across there project-feature-toggle buttons? I'm thinking we can create a nice shared partial view for these...

git grep -E "[^-]project-feature-toggle " -- *.haml

app/views/ci/variables/_variable_row.html.haml:          class: "js-project-feature-toggle project-feature-toggle #{'is-checked' if is_protected}",
app/views/ci/variables/_variable_row.html.haml:          class: "js-project-feature-toggle project-feature-toggle qa-variable-masked #{'is-checked' if is_masked}",
app/views/clusters/clusters/_form.html.haml:        class: "js-project-feature-toggle project-feature-toggle #{'is-checked' if @cluster.enabled?} #{'is-disabled' unless can?(current_user, :update_cluster, @cluster)}",
app/views/projects/pages_domains/_form.html.haml:          class: "js-project-feature-toggle project-feature-toggle mt-2 #{"is-checked" if auto_ssl_available_and_enabled}",
ee/app/views/groups/dependency_proxies/show.html.haml:            class: "js-project-feature-toggle project-feature-toggle #{'is-checked' if @dependency_proxy.enabled?}",
ee/app/views/groups/saml_providers/_form.html.haml:          class: "js-project-feature-toggle project-feature-toggle d-inline #{'is-checked' if saml_provider.enabled?}",
ee/app/views/groups/saml_providers/_form.html.haml:            class: "js-project-feature-toggle js-group-saml-enforced-sso-toggle project-feature-toggle d-inline qa-enforced-sso-toggle-button #{'is-checked' if saml_provider.enforced_sso?}",
ee/app/views/groups/saml_providers/_form.html.haml:            class: "js-project-feature-toggle js-group-saml-enforced-group-managed-accounts-toggle project-feature-toggle d-inline #{'is-checked' if saml_provider.enforced_group_managed_accounts?}",
ee/app/views/projects/protected_branches/ee/_code_owner_approval_form.html.haml:        class: "js-code-owner-toggle project-feature-toggle is-checked",
ee/app/views/projects/protected_branches/ee/_code_owner_approval_table.html.haml:      class: "js-code-owner-toggle project-feature-toggle mr-5 #{'is-checked' if protected_branch.code_owner_approval_required}",