[FIX] web: missing currency symbol on kanban column

[ndd-odoo]

Close https://github.com/odoo/odoo/issues/174408

• STEP TO REPRODUCE: go to crm -> kanban mode -> see each column and find no currency symbol, only amount display unlike in v15
• PROBLEM: The issue is deeper than the missing currency symbol. For now, we display the aggregate value but we don't know if all records share the same currency or not. If not, the displayed value makes no sense. The problem is different from the list case, because here, the sum is computed server side (by the read_group), on all records of the column (ignoring the limit). In the list case, this is the sum of the displayed records. We compute it client side, and we know the currency of each of those records, so it's easier.
• SOLUTION: Do same like in list view display 0 value (why 0 because the props require numeric value) and a title 'Different currencies cannot be aggregated'

Description of the issue/feature this PR addresses:

Current behavior before PR:

Desired behavior after PR is merged:

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