`brev create` and `brev search` flags for processor architecture are inconsistent

[brycelelbach]

The flags for specifying the processor architecture are inconsistent:

• --arch: CPU arch.
• --min-capability: Minimum GPU arch.

Suggestion:

• --cpu-arch: CPU arch.
• --gpu-arch: Exact GPU arch.
• --min-gpu-arch: Minimum GPU arch.
• Keep the old flags around for compat, but deprecate them and leave them out of --help.