Fix MIME Type in Support Portal

[Casey_Grimes]

I recently needed to dig in a few old support cases and noticed something minor, but annoying:

MIME types (for Excel workbooks, at least!) are not properly set for asset downloads on cases. Can someone update this? It's a little obnoxious to have to save and reopen rather than have it automatically open.

[Kenneth_Law]

Thank you for bringing this to our team's attention.  We'll take a look into this.