enable `doublezero address` to show the address of another keypair file

[dalalama]

the metrics-publisher key is another file that is stored on the device. In the configuration instructions, contributors need to use the pubkey of the metrics publisher but may not have the solana tools installed to determine the pubkey which this private key file represents.
also interestingly:

doublezero balance --keypair </path/keypair.json>

shows the balance of the key in this path.

doublezero address --keypair </path/keypair.json>

does not show the pubkey of the private key in this path. it shows the pubkey of the id.json file in the default path.