go:embed includes files at build time into a binary.
It doesn't work when consuming the SDK as a go module, since
the json files are not included in the module itself.

Instead of using embed, load the json file into the template
file and embed it directly (at generate time) into the
generated go files.

Signed-off-by: Andrea Frittoli <[email protected]>

The generator script allows for content field to be either
string or "References". This extends the generator to allow
for content fields being objects, with the limitations that
object must themselves be made of string fields alone.

Templates are extended to define new structs that hold the
object types and to use those types where needed.

Signed-off-by: Andrea Frittoli <[email protected]>

- Structured properties are now included as pointers.
  This is required so that the "omitempty" flags does not include
  them, when empty, in the rendered JSON.
- New test events
- New artifact signed event

Update the generator tool to support pointer objects. The full
type is now defined in the generator tool and templates are
simplified accordingly.

Signed-off-by: Andrea Frittoli <[email protected]>

Signed-off-by: Andrea Frittoli <[email protected]>