feat: zinit completion improvements

- Add all subcommand short & long flags
- Handle mutually exclusive options. For example, a user shouldn't be
  able to select the `--all` flag and a plugin in `zi delete` but should
  be able to select the `--yes` or `--quiet`
- Handle the zinit limitation of only taking one plugin in various
  commands (i.e., delete, uncompiled)

Examples:
- Don't show users plugins in the `zi delete` when they have already
  selected one to avoid an error.
- Only let the user select one flag option in `zinit time`.

Signed-off-by: Vladislav Doster <[email protected]>