add `--profile` to `sop encrypt`

It would be nice to be able to ask a sop implementation to encrypt with a specific profile as well.

A few open questions:

• is the current profile naming scheme acceptable for this? for example, could --profile=rfc4880 mean SEIPDv1 and --profile=draft-ietf-openpgp-crypto-refresh-08 mean SEIPDv2? Or should we consider a different profile naming convention?

• what should happen with the following command if Alice's cert doesn't support SEIPDv2?

sop encrypt --profile=ietf-openpgp-crypto-refresh-08 alice.cert