[Bug][Grid] ColumnMenu appears on group/expand columns

[vveesseelliinnaa]

Describe the bug
When enabling the columnMenu feature in the Grid component, it is also applied to special columns such as the group indicator column or the expand/collapse column. These columns are not user-defined and should not include the column menu.

This leads to a confusing UX where users can click the column menu icon on non-data columns, which serve internal purposes only.

To Reproduce

1. Go to https://stackblitz.com/edit/uj5myrrw-uaxzhef3?file=src%2Fmain.vue

Expected behavior
Only user-defined data columns should render the column menu icon. Internal columns (like group indicators or row expanders) should not display it.

Reported in TicketID: 1699857