better handling of tensorwise float8 recipe in configuration

[vkuzo]

Bug description

We need a follow-up on #808 . If --float8.recipe_name tensorwise is specified, we should handle the FSDP float8 all-gather, scale precompute, etc arguments properly instead of asserting that they aren't supported.

Versions

main branch

[tianyu-l]

Thanks for filing this issue.
That sounds cleaner to me! And we can have recipe_name default to “tensorwise”.