[Docs][PrebidServer] Adding `/version` doc (#1198)
[Docs][PrebidServer] Adding `/version` doc (#1198)

This CL introduces documentation for the `/version` admin endpoint.

Issue: #1197
sonobi/prebid.github.io,prebid/prebid.github.io,sonobi/prebid.github.io,sonobi/prebid.github.io,prebid/prebid.github.io,prebid/prebid.github.io