Modal service for zkey generation

[remicolin]

some zkeys are really long to build (especially for the dsc circuits) and ecdsa related ones will require more capabilities than mac allows.
A good idea would be to build them on a modal server such as we do for the dsc proving
I would probably look into zk-email codebase

[MPSxDev]

I would be happy to work on this issue.
In zk-email they used a mix of modal.com and aws for storage.
We could implement something similar. @remicolin