osm: infrastructure to synchronize external elements

config/packages/dev/web_profiler.yaml

src/Controller/Admin/ElementAdminBulkController.php

src/Document/Element.php

src/Document/WebhookPost.php

src/Services/ElementActionService.php

src/Services/ElementImportOneService.php

src/Services/ElementPendingService.php

src/Services/ElementSynchronizationService.php

src/Services/UserInteractionService.php

src/Services/WebhookService.php

templates/element-form/element-form.html.twig