Add a rocketpool update command

[jshufro]

N.B. The last commit is utterly boring conversions of prompt.Confirm(fmt.Sprintf(...)) to just prompt.Confirm(). It was created with the help of AI. Without it, the tests fail due to lint errors.

The commits with meaty changes are these:

For testing, you will want to build the cli and then run rocketpool update --force, otherwise it won't replace itself because the version numbers will match (run rocketpool update as well to verify this).

After each time you run the command, the binary will be replaced by whatever is on github, so you will need to rerun the build to get back the functionality.

rocketpool update --force -y works to auto-accept prompts and always overwrite.

Please please please find a volunteer to test this on OSX. It should work, but I don't have the hw to test it.

[jshufro]

Adding signature verification and reopening

[nickdoherty]

Tested on OSX

λ ./rocketpool-cli update

Your detected os/architecture is darwin/arm64.

The cli at /Users/nickdoherty/Git/playground/smartnode/rocketpool-cli/rocketpool-cli will be replaced. Continue? [y/n]
y

Replacing the cli at /Users/nickdoherty/Git/playground/smartnode/rocketpool-cli/rocketpool-cli with the latest version...
Downloading the new binary from https://github.com/rocket-pool/smartnode/releases/latest/download/rocketpool-cli-darwin-arm64

Verifying the binary signature
Downloading the signature from https://github.com/rocket-pool/smartnode/releases/latest/download/rocketpool-cli-darwin-arm64.sig
Signed by 651023D62E70B5DD
  Fornax <dante@rocketpool.net>
You are already on the latest version of smartnode: 1.19.4.

λ ./rocketpool-cli update --force --y

Your detected os/architecture is darwin/arm64.

Replacing the cli at /Users/nickdoherty/Git/playground/smartnode/rocketpool-cli/rocketpool-cli with the latest version...
Downloading the new binary from https://github.com/rocket-pool/smartnode/releases/latest/download/rocketpool-cli-darwin-arm64

Verifying the binary signature
Downloading the signature from https://github.com/rocket-pool/smartnode/releases/latest/download/rocketpool-cli-darwin-arm64.sig
Signed by 651023D62E70B5DD
  Fornax <dante@rocketpool.net>
Updating from 1.19.4 to 1.19.4

The cli has been updated.

LGTM