Use hash of attachment url as id.

Pretty hacky, let's see if we can get away with this.

lib/pleroma/web/mastodon_api/views/status_view.ex

@@ -61,8 +61,10 @@ def render("attachment.json", %{attachment: attachment}) do
       true -> "unknown"
     end
 
+    << hash_id::32, _rest::binary >> = :crypto.hash(:md5, href)
+
     %{
-      id: attachment["uuid"],
+      id: attachment["id"] || hash_id,
       url: href,
       remote_url: href,
       preview_url: href,

test/web/mastodon_api/status_view_test.exs

@@ -65,7 +65,7 @@ test "attachments" do
     }
 
     expected = %{
-      id: 6,
+      id: 1638338801,
       type: "image",
       url: "someurl",
       remote_url: "someurl",