Allow user to select an existing key for a new deploy alias

[Isaac-DeFrain]

Describe the problem

I added the ability to set the key in an existing deploy alias (among other things), but it would be nice to have the ability to select an existing key when creating a deploy alias instead. I am not familiar enough with yargs to add this feature (I tried but was unsuccessful).

Describe the proposed solution

Instead of always generating a new keypair for a deploy alias, include an option to choose from existing keys.

Alternatives considered

No response

Importance

nice to have

Additional Information

No response