Xdebug command fails on composable images

[jchaffer]

The upsun xdebug command fails on projects that have been updated to the new composable image syntax, because the YAML structure has changed and the command looks only for the old syntax.

Before:

runtime:
  extensions:
    ...
  xdebug:
    idekey: <my_key>

After:

stack:
  runtimes:
    - 'php@8.4':
        extensions:
          ...
        xdebug:
          idekey: <my_key>

In the command, the path to the idekey is fixed:

// legacy/src/Command/Environment/EnvironmentXdebugCommand.php, line 89
$ideKey = $config['runtime']['xdebug']['idekey'] ?? '';

This needs to be updated to also look for the idekey nested inside stack. The rest of the code works unchanged in either scenario.