Add server/cache support to gaeconfig.

appengine/gaemiddleware/context.go

Index: appengine/gaemiddleware/context.go
diff --git a/appengine/gaemiddleware/context.go b/appengine/gaemiddleware/context.go
index d4215448f58a997c4e2efd5add2ab7e2c58e5c42..27c66037ba8590eba7c576897e47a4252b205566 100644
--- a/appengine/gaemiddleware/context.go
+++ b/appengine/gaemiddleware/context.go
@@ -14,7 +14,6 @@ import (
 	"github.com/luci/gae/impl/prod"
 	"github.com/luci/gae/service/urlfetch"
 
-	"github.com/luci/luci-go/common/config"
 	"github.com/luci/luci-go/common/data/caching/cacheContext"
 	"github.com/luci/luci-go/common/data/caching/proccache"
 	"github.com/luci/luci-go/common/logging"
@@ -28,10 +27,10 @@ import (
 	"github.com/luci/luci-go/appengine/gaeauth/client"
 	"github.com/luci/luci-go/appengine/gaeauth/server"
 	"github.com/luci/luci-go/appengine/gaeauth/server/gaesigner"
-	"github.com/luci/luci-go/appengine/gaeconfig"
 	"github.com/luci/luci-go/appengine/gaesecrets"
 	"github.com/luci/luci-go/appengine/gaesettings"
 	"github.com/luci/luci-go/appengine/tsmon"
+	"github.com/luci/luci-go/luci_config/appengine/gaeconfig"
 )
 
 var (
@@ -87,7 +86,7 @@ func WithProd(c context.Context, req *http.Request) context.Context {
 
 	// The rest of the service may use applied configuration.
 	c = proccache.Use(c, globalProcessCache)
-	c = config.SetImplementation(c, gaeconfig.New(c))
+	c = gaeconfig.Use(c)
 	c = gaesecrets.Use(c, nil)
 	c = auth.SetConfig(c, globalAuthConfig)