[FIX] purchase_requisition: add context to vendor_id

partners for the vendor_id field on purchase.requisition (purchase agreement)
form view was not restricted to vendor partners. Also added default values for
on-the-fly creation.

addons/purchase_requisition/purchase_requisition_view.xml

@@ -131,7 +131,7 @@
                     <group>
                         <field name="user_id" attrs="{'readonly': [('state','not in',('draft','in_progress','open'))]}"/>
                         <field name="type_id" attrs="{'readonly': [('state','not in',('draft','in_progress','open'))]}" widget="selection"/>
-                        <field name="vendor_id"/>
+                        <field name="vendor_id" context="{'search_default_supplier':1, 'default_supplier':1, 'default_customer':0}" domain="[('supplier','=',True)]"/>
                         <field name="account_analytic_id" colspan="2" groups="purchase.group_analytic_accounting" attrs="{'readonly': [('state','not in',('draft'))]}"/>
                     </group>
                     <group>