tech-debt(ssh): Hard-coded midi-ssh

[VoVAllen]

Currently the SSH is hard-coded at examples/ssh_keypairs. We may need to make it flexible to configure.

[gaocegege]

How about https://github.com/tensorchord/MIDI/blob/main/pkg/remote/ssh/key.go#L3 ? Is it also used as a hard-coded string?

[VoVAllen]

@gaocegege Where does this come from? And where's the public key?

[gaocegege]

I do not know. I will dive into the code.

[gaocegege]

#dibs

[gaocegege]

I think we can deliver the binary in the Github release, then download the binary there instead of using the one in bin/

It can be cached in the ~/.midi/cache.

[gaocegege]

I will open a new issue to keep track of the key problem. The hard coded ssh binary is removed in #73

[gaocegege]

The default ssh download URL is not always public, we need to use the public URL. And we should not hard code the version.