Send activity signals during non-interactive codespace SSH command

[dmgardiner25]

We have an internal team trying to use the CLI for a long-running test in a codespace that doesn't print anything to stdout so our activity signal logic thinks there is no activity and shuts down the codespace before the test completes. This PR adds functionality to cover this case by continuously sending a keepAlive activity to the codespace if we set a flag to do so (in this case, when we detect a non-interactive SSH command, but this can be used elsewhere).

[cliAutomation]

Hi! Thanks for the pull request. Please ensure that this change is linked to an issue by mentioning an issue number in the description of the pull request. If this pull request would close the issue, please put the word 'Fixes' before the issue number somewhere in the pull request body. If this is a tiny change like fixing a typo, feel free to ignore this message.

[cmbrose]

@dmgardiner25 thanks for this! This looks like it will work, I had an alternative approach in mind where instead of pushing down into Shell() we pull the command parsing up. Something like below.

Just a suggestion :) but it feels a little cleaner to me to avoid needing the chan and goroutine listener

// --- rpc/ssh.go

// Make ParseSSHArgs public
func ParseSSHArgs(args []string) (flags, command []string, err error) {
    // ...
}

// Pass `flags` and `command` separately now so that we don't have to re-parse
// (Optionally, could make a wrapper object)
func Shell(
    ctx context.Context,
    p printer,
    flags []string,
    command []string,
    port int,
    destination string,
    printConnDetails bool,
) error {
    // ...
}

// --- cmd/ssh.go

// Use the newly-public parser
flags, command, err := codespaces.ParseSSHArgs(args)
// check err ...

// Check if we are running non-interactively
if command != nil {
    invoker.KeepAlive()
} 

// Pass the parsed args back into Shell
err = codespaces.Shell(ctx, keepAliveOverride, a.errLogger, flags, command, localSSHServerPort, connectDestination, opts.printConnDetails)

[dmgardiner25]

@cmbrose Good idea! I updated things to do just that.