Add Radius (https://radapp.io) feature collection (#339)

Co-authored-by: Álvaro Rausell Guiard <[email protected]>

Author: rynowak

_data/collection-index.yml

@@ -638,6 +638,11 @@
   contact: https://github.com/hsm207/devcontainer-templates/issues
   repository: https://github.com/hsm207/devcontainer-templates
   ociReference: ghcr.io/hsm207/devcontainer-templates
+- name: Radius Features (https://radapp.io/)
+  maintainer: radius-project
+  contact: https://github.com/radius-project/radius/issues
+  repository: https://github.com/radius-project/radius
+  ociReference: ghcr.io/radius-project/devcontainer-features
 - name: Dev Container Features by CASL0
   maintainer: CASL0
   contact: https://github.com/CASL0/devcontainer-features/issues