`--sftp=pub-key-algos=...` specifies the supported client public key
authentication algorithms. Note that this doesn't include certificate types
since those use the underlying algorithm. This list is sent to the client if
it supports the server-sig-algs extension. Order is irrelevant.

Valid values
```
ssh-ed25519
******@****.***
******@****.***
ecdsa-sha2-nistp256
ecdsa-sha2-nistp384
ecdsa-sha2-nistp521