spin targets command to list/update envs

[itowlson]

Fixes #3621.

$ spin targets list
akamai-functions
spin-up@3.2
spin-up@3.4
spin-up@3.5
spin-up@3.6

$ spin targets update
Target environments updated

Reviewers are advised to strap themselves in for a rollercoaster thrill ride of high-stakes sorting code.

[fibonacci1729]

I think a neat followup maybe would be a spin targets check for devs that didnt include a -E when scaffolding but want to answer the question : "can I deploy this to X?"

In any case, ill review this in the AM.

THANK YOU