[RFC] sale_timesheet_line_exclude: add group on `exclude_from_sale_order` field

[sbidoul]

I propose adding a security group on the exclude_from_sale_order field.

This field is quite sensitive since regular timesheet user are able to silently make their time not invoiceable.

In many situations, this decision is the responsibility of people with sales responsibility.

@alexey-pelykh as author of this module, what do you think?

[alexey-pelykh]

@sbidoul Great idea!

[sbidoul]

There you go: #707