Use getopt for parsing command-line arguments

[jawnsy]

We wrote our own argument-parsing code: https://github.com/cdr/code-server/blob/385be36dea427a3311fba440fb7e06fda66e864d/install.sh#L155-L162

It would be better to switch to getopt to simplify this, so that we don't our own custom code, and so that we support all the constructs that people expect (no value allowed, mandatory value, optional value)

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no activity occurs in the next 5 days.

[jsjoeio]

not stale