updating image paths with host var, plus other changes

[jdcmsd]

Changes:

• Updated Laravel DOTCMS_API_TOKEN to DOTCMS_API_KEY
  • This fixes the key mismatch while maintaining consistency with the Symfony library.
• On Laravel side, replaced hard-coded demo-site URL in image path with env('DOTCMS_HOST')
• On Symfony side, the app.environment syntax is preferred, but Claude suggested instead passing a new host variable by defining it in DotCMSExtension.php, so I went with that option.