Add /legacy/pagecounts endpoint to v1/metrics
Add /legacy/pagecounts endpoint to v1/metrics

AQS provide a new endpoint for aggregated legacy pagecounts.
This patch adds the restbase part of iti, i.e. adds an endpoint
to forward requests to AQS in v1/metrics.yaml.

wikimedia/mediawiki-services-restbase,gwicke/restbase,Pchelolo/restbase,d00rman/restbase,cscott/restbase,gwicke/restbase,milimetric/restbase,wikimedia/restbase,eevans/restbase,Pchelolo/restbase,wikimedia/mediawiki-services-restbase,eevans/restbase,d00rman/restbase,cscott/restbase,wikimedia/restbase,milimetric/restbase