In the sign application, it appeared that when using the default signature
in a signature SignItem that was higher the stroke at the bottom was doubbled.
This was caused by the fact that the bottom stroke is always added to the
template and that the default signature image had it already.
In order to solve this, we have added a setting 'show-stroke' that allows
controlling the stroke presence in the signature.
Task Id 2216067
Closes#48529
Related odoo/enterprise#9538
Signed-off-by: Yannick Tivisse (yti) <yti@odoo.com>