Use a switch control to enable/disable features

We were using buttons with the "Enable" and "Disable" texts to
enable/disable settings. However, when machine learning settings were
introduced in commit 4d27bbeba, a switch control was introduced to
enable/disable them.

In order to keep the interface consistent, we're now using switch
controls in other sections where settings are enabled/disabled. We can
even use the same code in the machine learning settings as well.

We're also removing the confirmation dialog to enable/disable a setting,
since the dialog is really annoying when changing several settings and
this action can be undone immediately. The only setting which might need
a confirmation is the "Skip user verification" one; we might add it in
the future. Removing the confirmation here doesn't make things worse,
though; the "Are you sure?" confirmation dialog was also pretty useless
and users would most likely blindly accept it.

Note Capybara doesn't support finding a button by its `aria-labelledby`
atrribute. Ideally we'd write `click_button "Participatory budgeting"`
instead of `click_button "Yes"`, since from the user's point of view the
"Yes" or "No" texts aren't button labels but indicators of the status of
the setting. This makes the code a little brittle since tests would pass
even if the element referenced by `aria-labelledby` didn't exist.

app/components/admin/settings/featured_settings_form_component.html.erb

@@ -1,7 +1,5 @@
-<%= form_for([:admin, feature]) do |f| %>
+<%= form_for([:admin, feature], html: { class: "featured-settings-form" }) do |f| %>
   <%= f.hidden_field :tab, id: dom_id(feature, :tab), value: tab if tab %>
-  <%= f.hidden_field :value, id: dom_id(feature, :value), value: (feature.enabled? ? "" : "active") %>
-  <%= f.submit(t("admin.settings.index.features.#{feature.enabled? ? "disable" : "enable"}"),
-               class: "button expanded #{feature.enabled? ? "hollow alert" : "success"}",
-               data: { confirm: t("admin.actions.confirm") }) %>
+  <%= f.hidden_field :value, id: dom_id(feature, :value), value: (enabled? ? "" : "active") %>
+  <%= f.button text, options %>
 <% end %>