feat: add serialNoColumnLabel option to customize serial number column header label

[fury0928]

Related to frappe/frappe#35724

Summary

• Add serialNoColumnLabel option to customize the serial number column header text
• Defaults to empty string for backwards compatibility with existing implementations

Usage

var datatable = new DataTable('#table', {
    serialNoColumn: true,
    serialNoColumnLabel: 'No.',  // Custom label
    columns: [...],
    data: [...]
});

Options

| Option              | Type   | Default | Description                           |
|---------------------|--------|---------|---------------------------------------|
| serialNoColumnLabel | String | ''      | Header label for serial number column |

To fix above issue, should I add `No.` as default to this table or should we edit from frappe frontend code?

[fury0928]

@sokumon @iamejaaz please review this PR
Thank you

[fury0928]

Good morning, @sokumon @nextchamp-saqib it'd be great if you can check this update, put for fixing the issue posted

[iamejaaz]

@sokumon Could you please check, when you have some time?