feat(actions)!: add RUN_RETENTION_DAYS to delete old action runs (#38855)

Gitea keeps completed Actions runs forever. Artifacts and logs expire on
their own schedule, but the run rows never go away, so `action_run` and
its child tables grow without bound.

Adds `RUN_RETENTION_DAYS` to delete completed runs along with their
jobs, tasks and anything the earlier expiries left behind. It defaults
to 400 days, matching how long GitHub keeps run history browsable. A
dedicated `cleanup_action_runs` cron task performs the cleanup, so
admins can schedule it separately from the nightly artifact and log
sweep.

`0` now means "keep forever" for all three retention settings, where
`LOG_RETENTION_DAYS` and `ARTIFACT_RETENTION_DAYS` previously took it
literally and deleted everything at the next sweep.

Docs: https://gitea.com/gitea/docs/pulls/502

----

## ⚠️ BREAKING ⚠️

`RUN_RETENTION_DAYS` defaults to 400, so completed runs older than that
are deleted when the cron task next runs at midnight. Set
`RUN_RETENTION_DAYS = 0` before upgrading to keep all runs.

---------

Co-authored-by: bircni <bircni@icloud.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>

models/actions/run_list.go

@@ -11,6 +11,7 @@ import (
 	user_model "gitea.dev/models/user"
 	"gitea.dev/modules/container"
 	"gitea.dev/modules/optional"
+	"gitea.dev/modules/timeutil"
 	"gitea.dev/modules/translation"
 	webhook_module "gitea.dev/modules/webhook"
 
@@ -203,3 +204,14 @@ func GetActors(ctx context.Context, repoID int64) ([]*user_model.User, error) {
 		OrderBy(user_model.GetOrderByName()).
 		Find(&actors)
 }
+
+// FindOldestRuns returns up to limit runs in the given statuses created before olderThan, lowest id first.
+func FindOldestRuns(ctx context.Context, statuses []Status, olderThan timeutil.TimeStamp, limit int) ([]*ActionRun, error) {
+	runs := make([]*ActionRun, 0, limit)
+	return runs, db.GetEngine(ctx).
+		Where(builder.In("`action_run`.status", statuses)).
+		And(builder.Lt{"`action_run`.created": olderThan}).
+		OrderBy("`action_run`.`id` ASC").
+		Limit(limit).
+		Find(&runs)
+}