Fix: allow completion command to run without an Octopus login

[HuyPhanNguyen]

Background

octopus completion <shell> is a local Cobra command that prints a shell completion script; it never contacts the server. But commandDoesNotRequireClient in cmd/octopus/main.go doesn't include it, so when the user hasn't run octopus login the client factory fails to build and the CLI exits with code 3, printing the config banner to stdout instead of the script. Piping that into Invoke-Expression then fails with The term 'Work' is not recognized. The same gap hits Cobra's hidden __complete/__completeNoDesc helpers, which the shell calls on every Tab press — so completions stay broken when not logged in even after installing them.

Results

Adds completion, __complete, and __completeNoDesc to commandDoesNotRequireClient so completion works without a login.

Fixes FD-555
Fixes #611

Before

Not logged in:

$ octopus completion powershell
Work seamlessly with Octopus Deploy from the command line.
... (banner) ...
# exit code 3, nothing on stderr

octopus completion powershell | Out-String | Invoke-Expression → The term 'Work' is not recognized.

After

Not logged in:

$ octopus completion powershell
# powershell completion for octopus ...
Register-ArgumentCompleter -CommandName 'octopus' -ScriptBlock $__octopusCompleterBlock
# exit code 0

octopus __complete "" also returns the command list (exit 0) instead of failing.

Testing

• Added a unit test covering the completion commands in commandDoesNotRequireClient.
• Manually verified against a build: unauthenticated completion powershell and __complete now exit 0; the ... | Out-String | Invoke-Expression command runs clean.

Note: this fixes the not-logged-in failure only. A separate report that tab-completion doesn't fire in Windows PowerShell 5.1 (when logged in) is not addressed here.