add legacy URL support for non-maven repositories

Nexus 2 Legacy URL activation support ( content/ ) was added in Nexus 3 as per NEXUS-9976

Support for /service/local/nuget/<repoid> style urls was omitted however. This means that NuGet repository clients must change their repository URLs to the new Nexus 3 style before Nexus 3 can work. ( repository/<repoid> )

Expected

NuGet was the only repository format that required special URLs in Nexus 2. Add support for these special URLs in Nexus 3 to make upgrade more seamless.

Note
We should address site repos when we do this as well, since they're mapped under content/sites in NXRM2.