Existing app icon request button

[peter-garvin]

We'd like a way for users to request unassigned app icons similar to how UI icons are downloaded:

• This would need to be for Unassigned icons only
• If possible, it would be nice to have a light tooltip on dark theme, and a dark tooltip on light. If not, dark tooltip will work
• needs to link to: https://github.ibm.com/brand/App-icons/issues/new?template=existing-app-icon-request.md

#759

[mjabbink]

@peter-garvin SHould it be a different icon? I’m fine with this but just wondering if there might be a better one for making a request on github.