Fix the import of vendor bills that use per-line ScontoMaggiorazione.
The discount/surcharge should be applied to the price unit before taxes, instead of summed and subtracted from the total.

#### Correct
| Product   | Qty | Unit Price | Discount | VAT % | Formula                          | Total     |
|-----------|-----|------------|----------|-------|----------------------------------|-----------|
| Product 1 | 2   | 5.00       | 3.00     | 22%   | `2 * (5 - 3) * 1.22`             | 4.88      |
| Product 2 | 1   | 10.00      | 3.00     | 10%   | `1 * (10 - 3) * 1.10`            | 7.70      |
|           |     |            |          |       |                                  | **12.58** |


#### Before 
the scontomaggiorazione is not managed line by line.
We have to manage line by line because the ScontoMaggiorazione should decrease the "Imponibile" and than calculate the amount tax line by line because each line can have different tax % .

ATTENTION: the ScontoMaggiorazione on ImportoTotaleDocumento is not the sum of the ScontoMaggiorazione on the lines. It is a discount on the amount tax included

#PURPOSE:
 - Currently is the user is promoted as admin for accounting and he/she is try
   to generate/regenerate or view the gst report following Error is thrown.
 - Access Error

    ```Uh-oh! Looks like you have stumbled upon some top-secret records.

       Sorry, Marc Demo (id=5) doesn't have 'read' access to:
         - Document (documents.document)```

#STEPS TO REPRODUCE
  1) Install necessary modules for indian accounting localization.
  2) Enable GST E-Filing & Matching Feature from account's configuration.
  3) Go to Settings -> User & Companies -> Users
  4) Click new if no user is there other then administrator else click on
     another user.
  5) Under Access Rights section , inside Accounting select Administrator & Save.
  6) Now log in as new user in another tab.
  7) Go to Accounting -> Reporting under 'India' section click on
     GST Return Period.
  8) Click on generate/regenerate or View option.
  9) The above shown error will be raised.

#SPECIFICATION:
- The issue is with documents access rights
- After promoting user to admin of accounting, the document's folder right is
  not properly assign to user.
- fix this by giving rights of GSTR folder to user if user is in accounting 
  manager group.
  
task-4770583

### Issue:

The current design of the 'pruchase' approval requests makes it possible to create and confirm requests for RFQ's that can not be validated down the road leading to dead un-usable records.

To be more precise, the `product_id` field is not required to be set on `product_line_ids` of `approval.request` of the `purchase` type: https://github.com/odoo/enterprise/blob/fe983e9874409415a1cf4f1a822173aec454ca06/approvals_purchase/views/approval_product_line_views.xml#L12 The initial idea behind this design choice was to let the approver (who might have more access rights than the user making the request) create and set a `product_id` based on the line description before validating the request. However, this process can not be performed since, the product lines become readonly once the request has been confirmed: https://github.com/odoo/enterprise/blob/fe983e9874409415a1cf4f1a822173aec454ca06/approvals/views/approval_request_views.xml#L184-L189 In particular, the approver will never be able edit them nor can he generate the related order as this action raises a user error: https://github.com/odoo/enterprise/blob/fe983e9874409415a1cf4f1a822173aec454ca06/approvals_purchase/models/approval_request.py#L21-L22

### Steps to reproduce:

With Marc Demo
- Approvals > Create RFQ's > New Request
- Add a line wihtout product but with a description and quantity
- Set Mitchell Admin as approver and submit the request
- Login with Mitchell > Approvals > Manager > Approvals to review
- Try to approve the request
> A user error is raised: You must select a product for each line of
requested products.
> Since the line is readonly you are stuck.

opw-4815115