feat(11.1-05): add the acme.blog walkthrough plugin with its model, migration and posts route

- docs/examples/blog: scaffolder output for acme.blog (make:plugin, make:model)
  in the root module, with a Post model, a fill allow-list and NewPost, the
  create migration and GET /api/blog/posts paginated through lagoon
- short tests activate the plugin, check the route with surf, the fill
  allow-list and the migration order
- docs/setup/porting-a-plugin.md: registration, model, migrations and routes
  sections with src= copies of the plugin
- TestDocsRequiredPages requires setup/porting-a-plugin

docs/examples/blog/models/post.go

@@ -0,0 +1,37 @@
+// Code generated by summer make. DO NOT EDIT.
+
+package models
+
+import (
+	"time"
+
+	"git.golem15.com/golem15/summercms/modules/lagoon"
+)
+
+// Post is a blog post, the Go form of the WinterCMS Acme\Blog\Models\Post
+// model.
+type Post struct {
+	ID        uint      `gorm:"column:id;primaryKey"`
+	Title     string    `gorm:"column:title"`
+	Slug      string    `gorm:"column:slug"`
+	Body      string    `gorm:"column:body"`
+	CreatedAt time.Time `gorm:"column:created_at"`
+	UpdatedAt time.Time `gorm:"column:updated_at"`
+}
+
+// TableName keeps the WinterCMS table name.
+func (Post) TableName() string { return "acme_blog_posts" }
+
+// Fillable is the Go form of $fillable: the only columns lagoon.Fill may
+// set from a request.
+func (Post) Fillable() []string { return []string{"title", "slug", "body"} }
+
+// NewPost is the Go form of Post::make($input): it copies only the fillable
+// keys of input onto a new post and drops the rest, such as id.
+func NewPost(input map[string]any) (*Post, error) {
+	post := &Post{}
+	if err := lagoon.Fill(post, post.Fillable(), input, true); err != nil {
+		return nil, err
+	}
+	return post, nil
+}