Fix bfcl so that instances do not explode in size, and all cards yield recipes that pass _source_to_dataset

[dafnapension]

closes https://github.com/IBM/unitxt/issues/1894 and also fixes small issues that prevent the recipes generated from the bfcl cards prepared to be well processed by _source_to_dataset (mainly schema issues)

Errors before the fix:
bfcl_main.pdf

No errors after, and instance sizes are reasonable:
bfcl_fix.pdf