Modify .sshconfig for axiom instances

[thapr0digy]

Using the changes from PR #614, I added another function to only pull axiom created instances into the sshconfig. It'll allow for listing of all instances with axiom-ls, but axiom-ssh and axiom-account will use the new function.

The other choice is to just modify the "instances" function itself, but I haven't tested that.

[0xtavian]

@thapr0digy had to replace the function with doctl compute droplet list -o json | jq -r 'select( .[].image.name | startswith("axiom"))' to get it working as expected. Still debating and testing the concept, but wont be merging as-is. thank you!