[Attachment] Move Controller and Entities to a Component

There's no problem in having the templates in the core

docs/developer/src/cache.md

@@ -35,7 +35,7 @@ public static function getAvatarFileInfo(int $gsactor_id): array
             Cache::get("avatar-file-info-{$gsactor_id}",
                 function () use ($gsactor_id) {
                     return DB::dql('select f.file_hash, f.mimetype, f.title ' .
-                        'from App\Entity\Attachment f ' .
+                        'from Component\Attachment\Entity\Attachment f ' .
                         'join App\Entity\Avatar a with f.id = a.attachment_id ' .
                         'where a.gsactor_id = :gsactor_id',
                         ['gsactor_id' => $gsactor_id]);

docs/developer/src/storage.md

@@ -68,7 +68,7 @@ Simple enough.
 
 ### Attachments: Storing a reference in database
 Finally, you need a way to refer to previous files.
-GNU social calls that representation of `App\Entity\Attachment`.
+GNU social calls that representation of `Component\Attachment\Entity\Attachment`.
 If a note refers to an `Attachment` then you can link them
 using the entity `AttachmentToNote`. 
 
@@ -97,7 +97,7 @@ can be generated from files. And `StoreRemoteMedia` to understand how to generat
 them from URLs.
 
 The controller asking for them is the `App\Controller\Attachment::attachment_thumbnail` with
-a call to `App\Entity\AttachmentThumbnail::getOrCreate()`.
+a call to `Component\Attachment\Entity\AttachmentThumbnail::getOrCreate()`.
 
 ## Trade-offs between decoupling and complexity