Currently, the system restricts fiscal document types for both sales and 
purchases based on the company’s VAT affiliation, which prevents 
valid vendor bills from being recorded.

**Steps to reproduce:**
- Install the `l10n_gt_edi` module and switch to a `GT company`.
- Navigate to Accounting > Vendors > Bills.
- Create a vendor bill.
- Try to select a document type such as `FPEQ` or `FCAP`.

**Observation:**
The system hides valid vendor document types (e.g., `FPEQ`, `FCAP`) 
if they do not match the company’s VAT affiliation.

**Root Cause:**
At [1], the method `_compute_l10n_gt_edi_available_doc_types` 
filters document types using the company’s VAT affiliation 
(`l10n_gt_edi_vat_affiliation`) for all move types.

This logic is correct for sales (where the company is the issuer), 
but incorrect for purchases (where the vendor determines the document 
type). As a result, valid purchase document types are wrongly excluded.

**Fix:**
This commit updates the computation logic to:
- Apply affiliation-based filtering only for sales (`out_*`).
- Bypass the restriction for purchases (`in_*`), allowing all valid document types.

This ensures that vendor bills can include any legally valid document 
type regardless of the company’s affiliation, while preserving the 
existing restrictions for sales workflows.

[1]:
https://github.com/odoo/enterprise/blob/7792926504a823590fbbe574a96994002a92fc17/l10n_gt_edi/models/account_move.py#L162-L166

opw-6099863

Forward-Port-Of: odoo/enterprise#120363
Forward-Port-Of: odoo/enterprise#113133