Add "available" attribute to recipes

[Satrat]

Fixes the error in this Asana ticket: https://app.asana.com/0/1204322589046915/1205549265505143/f

Adds an available attribute to Recipes that provides a list of recipe names. This is needed by the sparsify.run sparse transfer

Testing

Confirmed the command failing in the ticket runs:

sparsify.run sparse-transfer --use-case image-classification --data imagenette --optim-level 0.5

Also updated unit tests to test the new property

[rahul-tuli]

Nice clean diff!