Icon Sprite URL needs to be local even if asset_host is set

What does this MR do?

It will return a local URL for our SVG Sprite even if an asset_host is set. Because SVG sprites don't work due to Browser XML concerns not cross domain so we can't serve them over the CDN.

This is blocking turning on the CDN, so we should get it to production asap, hence ~"Pick into 10.2"

Why was this MR needed?

To unblock our move for the CDN

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered

What are the relevant issue numbers?