feat: Notifiers CRUD (#337)

* introduce scaffold for new models

* wip: shoutrrr wrapper (may remove)

* update schema files

* gen: ent code

* gen: migrations

* go mod tidy

* add group_id to notifier

* db migration

* new mapper helpers

* notifier repo

* introduce experimental adapter pattern for hdlrs

* refactor adapters to fit more common use cases

* new routes for notifiers

* update errors to fix validation panic

* go tidy

* reverse checkbox label display

* wip: notifiers UI

* use badges instead of text

* improve documentation

* add scaffold schema reference

* remove notifier service

* refactor schema folder

* support group edges via scaffold

* delete test file

* include link to API docs

* audit and update documentation + improve format

* refactor schema edges

* refactor

* add custom validator

* set validate + order fields by name

* fix failing tests

backend/internal/data/ent/schema/notifier.go

@@ -0,0 +1,51 @@
+package schema
+
+import (
+	"entgo.io/ent"
+	"entgo.io/ent/schema/field"
+	"entgo.io/ent/schema/index"
+
+	"github.com/hay-kot/homebox/backend/internal/data/ent/schema/mixins"
+)
+
+type Notifier struct {
+	ent.Schema
+}
+
+func (Notifier) Mixin() []ent.Mixin {
+	return []ent.Mixin{
+		mixins.BaseMixin{},
+		GroupMixin{
+			ref:   "notifiers",
+			field: "group_id",
+		},
+		UserMixin{
+			ref:   "notifiers",
+			field: "user_id",
+		},
+	}
+}
+
+// Fields of the Notifier.
+func (Notifier) Fields() []ent.Field {
+	return []ent.Field{
+		field.String("name").
+			MaxLen(255).
+			NotEmpty(),
+		field.String("url").
+			Sensitive().
+			MaxLen(2083). // supposed max length of URL
+			NotEmpty(),
+		field.Bool("is_active").
+			Default(true),
+	}
+}
+
+func (Notifier) Indexes() []ent.Index {
+	return []ent.Index{
+		index.Fields("user_id"),
+		index.Fields("user_id", "is_active"),
+		index.Fields("group_id"),
+		index.Fields("group_id", "is_active"),
+	}
+}