Provide formatting configuration for IDEs

[BenoitPerrot]

The default formatting rules in IntelliJ are different from the ones used in the codebase.

It's already something to have a maven plugin to enforce the coding style, but it would be even better to provide contributors with a configuration matching the rules enforced by the maven plugin.

[Ant-hem]

We could agree on an .editorconfig file it's supported by most IDEs