Auth: Move Team service to SignedInUserInterface (#72674)

* move SignedInUser to specific file

* add primitive interface for signedInUser

pkg/services/auth/identity/requester.go

@@ -0,0 +1,9 @@
+package identity
+
+type Requester interface {
+	GetIsGrafanaAdmin() bool
+	GetLogin() string
+	GetOrgID() int64
+	GetPermissions(orgID int64) map[string][]string
+	IsNil() bool
+}