🐛(react) allow to set column size for data grid without header

Currently, to set the width of column we define a width to the
corresponding header cell. But DataGrid components allows to not render
header rows so in this case, the size is not set. In order to fix that,
if header is not rendered, we set width of cell to the corresponding
column.

.changeset/grumpy-cobras-roll.md

@@ -0,0 +1,5 @@
+---
+"@openfun/cunningham-react": patch
+---
+
+allow to set column size for data grid without header