CLI - Let users know if there's a new version available

[bfops]

Background

We'd like the CLI to let users know if they'd be able to upgrade.

Definition of Done

• When users run any command, try to check if there's an upgrade available on GitHub
  • Make a short timeout, to avoid hanging the CLI
  • If the request fails, assume there's no upgrade
  • If there's an upgrade available, print an informational message to the user before running the subcommand

[bfops]

note: this will only be impactful for the release after the one it's included in

[jdetter]

I would do whatever the gh command does because they have a good cadence for telling the user to upgrade.

[jdetter]

Rationale for making it a P1: More people will upgrade to the new release if we tell them it's available. Otherwise we are losing a bunch of users on previous releases who will just never upgrade because they don't know an update is available. Also from a customer support standpoint we want people to upgrade to get bug fixes ASAP.

[bfops]

#4250 will embed something like this into the spacetime version command, but users would only see it if they ran that command, which I think is insufficient to call this done.