[ADD] pos_salesperson: added salesperson choosing button in POS

[abpa-odoo]

• inherited pos.order and pos.session add a Salesperson_id field in pos.order model to track assigned sales representatives.
• Loaded the hr.employee model in pos.session to access salesperson data.
• Created a 'SelectSalesperson' Button component for selecting a salesperson.
• Patched ControlButtons to include the salesperson selection option.
• created setSalesperson and getSalesperson functions in POS Order to manage salesperson .
• Displayed the salesperson on the billing screen .

[robodoo]

[adsh-odoo]

Also Task id is missing in the commit message.