Billing (#1269)

* Change env SELF_HOSTING_ENABLED to SELF_HOSTED

* Initial Stripe implementation

* Fix portal link

* Use webhook signatures

* Migrated to new Stripe gem conventions

Also updated resource routing

* Added faraday-multipart gem to resolve middleware notice

* Merge fix

* Merge fix

* Temporary upgrade prompt for early access

* Lint fix

* i18n fixes

* Remove catch-all rescue

* Update .env.example

app/views/settings/_nav.html.erb

@@ -26,6 +26,9 @@
             <%= sidebar_link_to t(".self_hosting_label"), settings_hosting_path, icon: "database" %>
           </li>
         <% end %>
+        <li>
+          <%= sidebar_link_to t(".billing_label"), settings_billing_path, icon: "circle-dollar-sign" %>
+        </li>
         <li>
           <%= sidebar_link_to t(".accounts_label"), accounts_path, icon: "layers" %>
         </li>