[FIX] stock_dropshipping: add dropship to domain

**Current behavior:**
When making a new RFQ, dropship is not an available selection
for the 'Deliver To' option.

**Expected behavior:**
As on previous versions, you should 'dropship' should be
selectable here which reveals a sub-selection to select the
customer who should receive the shipment.

**Steps to reproduce:**
1. Enable `Dropshipping` in Purchase settings as well as
     `Storage Locations` in Inventory settings

2. Create a new RFQ, observe that in the 'Deliver To' dropdown
     there is no way to select a dropship option

**Cause of the issue:**
Dropshipping was made into a discrete `stock.picking.type`.code
and the domain that constrains the selection menu options is not
modified to accomodate this change.

**Fix:**
Update the domain to show picking types that have the dropship
code.

opw-3764617

closes odoo/odoo#157548

X-original-commit: 3ea6e552bde90533f983689d786fee219e0e61ce
Signed-off-by: Djamel Touati (otd) <otd@odoo.com>
Signed-off-by: Vincent Ethan <etvi@odoo.com>

addons/stock_dropshipping/views/purchase_order_views.xml

@@ -14,6 +14,11 @@
                     <field name="dropship_picking_count" widget="statinfo" string="Dropship"/>
                 </button>
             </xpath>
+            <xpath expr="//field[@name='picking_type_id']" position="attributes">
+                <attribute name="domain">
+                    [('code', 'in', ('incoming', 'dropship')), '|', ('warehouse_id', '=', False), ('warehouse_id.company_id', '=', company_id)]
+                </attribute>
+            </xpath>
         </field>
     </record>
 </odoo>