[MNG-7377] Add .vscode/ to .gitignore

VS Code creates directories with configurations in project directories. This
is usually fine, but triggers the `apache-rat` license alarms and future
VS Code users might accidentally commit the directory.

To solve the alarm and avoid future issues, we add it to .gitignore.

This closes #646
diff --git a/.gitignore b/.gitignore
index 3404996..0a2cc2d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -15,3 +15,4 @@
 .java-version
 .checkstyle
 .factorypath
+.vscode/