Ignore git related files from docker build (#16282)

Co-authored-by: Yamagishi Kazutoshi <ykzts@desire.sh>

.dockerignore

@@ -1,6 +1,10 @@
 .bundle
 .env
 .env.*
+.git
+.gitattributes
+.gitignore
+.github
 public/system
 public/assets
 public/packs