Add .editorcofing (open-telemetry#8)

To have clean consistent formatting

Author: dmitryax

.editorconfig

@@ -0,0 +1,12 @@
+# https://editorconfig.org
+
+root = true
+
+[*]
+trim_trailing_whitespace = true
+insert_final_newline = true
+charset = utf-8
+
+[*.{json,yaml}]
+indent_style = space
+indent_size = 2