feat(docker): associate 'Containerfile' with 'dockerfile' filetype (#5974)

## Description

'Containerfile' [1] is a supported alternative name for container build
definitions. It is recognized by Docker and other container tools, and
can help clarify intent in multi-container repositories or
non-Docker-specific setups.

[1]:
https://github.com/containers/common/blob/main/docs/Containerfile.5.md

## Checklist

- [x] I've read the
[CONTRIBUTING](https://github.com/LazyVim/LazyVim/blob/main/CONTRIBUTING.md)
guidelines.

lua/lazyvim/plugins/extras/lang/docker.lua

@@ -2,7 +2,14 @@ return {
   recommended = function()
     return LazyVim.extras.wants({
       ft = "dockerfile",
-      root = { "Dockerfile", "docker-compose.yml", "compose.yml", "docker-compose.yaml", "compose.yaml" },
+      root = {
+        "Dockerfile",
+        "Containerfile",
+        "docker-compose.yml",
+        "compose.yml",
+        "docker-compose.yaml",
+        "compose.yaml"
+      },
     })
   end,
   {