Licensing service (#19903)

* Licensing: supplies a service to handle licensing information

* Licensing: uses the license service further

Uses the license service instead of settings.isEnterprise:
- external team members
- saml
- usage stats

* Licensing: fixes broken tests due to new Licensing service dependency

* Licensing: fixes linting errors

* Licensing: exposes license expiry information to the frontend

pkg/extensions/main.go

@@ -6,6 +6,8 @@ import (
 
 	_ "github.com/crewjam/saml"
 	_ "github.com/gobwas/glob"
+	"github.com/grafana/grafana/pkg/models"
+	"github.com/grafana/grafana/pkg/registry"
 	_ "github.com/jung-kurt/gofpdf"
 	_ "github.com/robfig/cron"
 	_ "github.com/robfig/cron/v3"
@@ -13,4 +15,8 @@ import (
 	_ "gopkg.in/square/go-jose.v2"
 )
 
+func init() {
+	registry.RegisterService(&models.OSSLicensingService{})
+}
+
 var IsEnterprise bool = false