Reduce usage of db.DefaultContext (#27073)

Part of #27065

This reduces the usage of `db.DefaultContext`. I think I've got enough
files for the first PR. When this is merged, I will continue working on
this.

Considering how many files this PR affect, I hope it won't take to long
to merge, so I don't end up in the merge conflict hell.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/metrics/collector.go

@@ -7,6 +7,7 @@ import (
 	"runtime"
 
 	activities_model "code.gitea.io/gitea/models/activities"
+	"code.gitea.io/gitea/models/db"
 	"code.gitea.io/gitea/modules/setting"
 
 	"github.com/prometheus/client_golang/prometheus"
@@ -232,7 +233,7 @@ func (c Collector) Describe(ch chan<- *prometheus.Desc) {
 
 // Collect returns the metrics with values
 func (c Collector) Collect(ch chan<- prometheus.Metric) {
-	stats := activities_model.GetStatistic()
+	stats := activities_model.GetStatistic(db.DefaultContext)
 
 	ch <- prometheus.MustNewConstMetric(
 		c.Accesses,