Rename attestation-name

[ianlewis]

Fixes #654

generic generator:

• Refactors predicate-only generation to a separate generate command.
• Changes default provenance bundle file names to be in line with in-toto attestation bundle file naming conventions
• Changes the attestation-name input and outputs to provenance-name. The old name can be still used but is deprecated for now.
• Updated pre-submit tests to use new inputs

container workflow

• Updated to use the new generate command.

[laurentsimon]

Thanks!