[FR] add well-known mixin to let plugins define well-known urls (#12698)

* [FR] add well-known mixin to let plugins define well-known data entry points
Fixes #11741

* add built-in plugin for apis

* add test

* add decorator

* ignore default

* fix tests

* remove erronius decorator

* all well-known paths to security exception paths

* update test setup

* ignore escape paths

* add docs

* add more on security considerations

* add to nav

docs/mkdocs.yml

@@ -237,6 +237,7 @@ nav:
       - URL Mixin: plugins/mixins/urls.md
       - User Interface Mixin: plugins/mixins/ui.md
       - Validation Mixin: plugins/mixins/validation.md
+      - Well-Known Mixin: plugins/mixins/wellknown.md
     - Machines:
       - Overview: plugins/machines/overview.md
       - Label Printer: plugins/machines/label_printer.md