Add .editorconfig to harmonize indention

EditorConfig (https://editorconfig.org) helps maintain consistent coding
styles for multiple developers working on the same project across
various editors and IDEs.

.editorconfig

@@ -0,0 +1,13 @@
+root = true
+
+[*]
+end_of_line = lf
+insert_final_newline = true
+
+[*.java]
+indent_style = space
+indent_size = 2
+
+[*.gradle]
+indent_style = space
+indent_size = 4