DCB: Download not working correctly

Device Config download not working correctly.

• single file download sometimes has 'object [Object]' instead of actual Json text
• multi file download is not a valid tar.gz file

Issues:

• some mismatch between UI and Rest API code/assumptions. Rest API may work when called directly but not when called via UI
• CORS issues with UI accessing 'Content-Disposition' (which is not a CORS safelisted header) which is causing problems getting the correct 'content-type' and filename
• May need to send 'Access-Control-Expose-Headers' for 'Content-Disposition' or find another workaround