[FIX] web: fix the error that the name of the line is too long

- Currently the label of the lines is not limited to the number of characters. When the user gives a name that is too long, the graph will not be displayed.
- This commit limits the number of labels, if exceeded it will display as ...

closes odoo/odoo#95291

Signed-off-by: Mathieu Duckerts-Antoine <dam@odoo.com>