Adding SSH key generation inside Uploy

This commit, I added SSH key generation directly inside Uploy, which changed the setup flow quite a bit.

Before this, users had to generate an SSH key manually on the control plane machine, for example on my Mac, using ssh-keygen, then copy the key around themselves. It worked, but it felt like one of those setup steps that added friction for no real product reason.

Now the key pair can be generated from inside Uploy itself, and both the private key and public key are stored on the Uploy server. From the UX side, this feels much better. The setup is more guided, and users no longer have to leave the product just to prepare an SSH key manually. I also kept the option for users who already have their own private key, so the flow is more flexible now.

This was a nice product improvement because it made the SSH key setup feel less like raw infrastructure work and more like part of the platform itself… although it also made me think more seriously about how private keys should be stored and protected once Uploy becomes responsible for managing them.