Service Accounts: Implement basic usage stats (#46619)

* Stats: do not count SAs as users

* Stats: implement basic service account metrics

* Stats: do not count service account tokens as api keys

* Stats: fix metric names

* Stats: add SA stats test

* rename user to sa

pkg/services/serviceaccounts/database/stats.go

@@ -0,0 +1,37 @@
+package database
+
+import (
+	"context"
+
+	"github.com/grafana/grafana/pkg/services/sqlstore"
+)
+
+func (s *ServiceAccountsStoreImpl) GetUsageMetrics(ctx context.Context) (map[string]interface{}, error) {
+	stats := map[string]interface{}{"stats.serviceaccounts.enabled.count": int64(1)}
+
+	sb := &sqlstore.SQLBuilder{}
+	dialect := s.sqlStore.Dialect
+	sb.Write("SELECT ")
+	sb.Write(`(SELECT COUNT(*) FROM ` + dialect.Quote("user") +
+		` WHERE is_service_account = ` + dialect.BooleanStr(true) + `) AS serviceaccounts,`)
+	sb.Write(`(SELECT COUNT(*) FROM ` + dialect.Quote("api_key") +
+		` WHERE service_account_id IS NOT NULL ) AS serviceaccount_tokens`)
+
+	type saStats struct {
+		ServiceAccounts int64 `xorm:"serviceaccounts"`
+		Tokens          int64 `xorm:"serviceaccount_tokens"`
+	}
+
+	var sqlStats saStats
+	if err := s.sqlStore.WithDbSession(ctx, func(sess *sqlstore.DBSession) error {
+		_, err := sess.SQL(sb.GetSQLString(), sb.GetParams()...).Get(&sqlStats)
+		return err
+	}); err != nil {
+		return nil, err
+	}
+
+	stats["stats.serviceaccounts.count"] = sqlStats.ServiceAccounts
+	stats["stats.serviceaccounts.tokens.count"] = sqlStats.Tokens
+
+	return stats, nil
+}