Add support for Asset globs

Also finding that adding asset on a List, where not all components have an asset with that asset name, an error is shown.

As a part of this we should be able to validate whether a file truly exists, and add it conditionally.

Maybe consider adding a param to Asset attr that can ignore non existent files, or throw errors on missing files (default).

Of course, otherwise the Asset attr can be added to individual components/enum-case rather than an asset-attr thats echo'ed from the top of an enum.

For #3, for now, changed to exception if missing file, unless the asset is a glob in which no exceptions are thrown if nothing was found.