feat: Trivial default quota configuration

This adds a new configuration setting: `[quota.default].TOTAL`, which
will be used if no groups are configured for a particular user. The new
option makes it possible to entirely skip configuring quotas via the API
if all that one wants is a total size.

Signed-off-by: Gergely Nagy <forgejo@gergo.csillger.hu>

models/quota/default.go

@@ -0,0 +1,25 @@
+// Copyright 2024 The Forgejo Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package quota
+
+import (
+	"code.gitea.io/gitea/modules/setting"
+)
+
+func EvaluateDefault(used Used, forSubject LimitSubject) bool {
+	groups := GroupList{
+		&Group{
+			Name: "builtin-default-group",
+			Rules: []Rule{
+				{
+					Name:     "builtin-default-rule",
+					Limit:    setting.Quota.Default.Total,
+					Subjects: LimitSubjects{LimitSubjectSizeAll},
+				},
+			},
+		},
+	}
+
+	return groups.Evaluate(used, forSubject)
+}