Geo: Add Geo-secondary-specific routing in Workhorse

To do

• Determine where in the Workhorse code we should implement Geo-secondary-specific routing
• Implement Geo-secondary-specific routing
• Make Workhorse use Geo-secondary-specific routing if geo_proxy_url is present in the /api/v4/geo/proxy response
• Tests

Where does this fit in the epic?

Description	Issue
Add endpoint /api/v4/geo/proxy	#324664 (closed)	!63343 (merged)
Determine if this is a Geo Proxy by calling /api/v4/geo/proxy	#329670 (closed)	!60769 (merged)
If this is a Geo Proxy, then use the Geo Proxy routing table	#329672 (closed) You are here	!63321 (merged)
Before we can remove the environment variable, we must add caching of the result of the request	#329671 (closed)