reformat build.gradle.kts 2 indent

project uses 2 spaces indent, lf as line ending, utf-8. make it easier
to follow this rule by adding a .editorconfig file which vscode and
intellij respect out of the box.

.editorconfig

@@ -0,0 +1,13 @@
+# Editor configuration, see http://editorconfig.org
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+indent_size = 2
+indent_style = space
+trim_trailing_whitespace = true
+
+[*.md]
+max_line_length = off
+trim_trailing_whitespace = false