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/models/licensing.go

@@ -0,0 +1,30 @@
+package models
+
+type Licensing interface {
+	// HasValidLicense is true if a valid license exists
+	HasValidLicense() bool
+
+	// HasLicense is true if there is a license provided
+	HasLicense() bool
+
+	// Expiry returns the unix epoch timestamp when the license expires, or 0 if no valid license is provided
+	Expiry() int64
+}
+
+type OSSLicensingService struct{}
+
+func (OSSLicensingService) HasLicense() bool {
+	return false
+}
+
+func (OSSLicensingService) Expiry() int64 {
+	return 0
+}
+
+func (OSSLicensingService) Init() error {
+	return nil
+}
+
+func (OSSLicensingService) HasValidLicense() bool {
+	return false
+}