[ADD] l10n_tr_nilvera_einvoice_extended: Adding Nilvera E-Invoice Extension  
[ADD] l10n_tr_nilvera_einvoice_extended: Adding Tax Offices

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### Description of the issue/feature this PR addresses:

We do not support Withholding VAT (KDV Tevkifatı), Exemption Invoices, and Export Invoices (İhracat Faturaları) with our current e-invoicing solution in Türkiye. Those invoice types are legally important and required for both domestic and international sales for businesses. In addition, the inclusion of the Tax office in our current XML we send to Nilvera, both for `<cac:AccountingSupplierParty>` and `<cac:AccountingCustomerParty>`, is required by law.

This PR adds an extension module for Nilvera E-Invoicing. The purpose of this module is to extend the existing E-Invoicing functionality to support additional invoice types and scenarios to be compliant with the TR legal requirements.

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### Invoice Scenario:

**Basic**  
Invoice Type:
- Sales  
- Withholding  
- Tax Exempt  
- Registered for Export  

**Export**  
Invoice Type:
- Tax Exempt  

**Public**  
Invoice Type:
- Sales  
- Withholding  
- Tax Exempt  
- Registered for Export  

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### Current behavior before PR:

We don't support a scenario-based system to comply with TR legal requirements.

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### Desired behavior after PR is merged:

We support a scenario-based system to comply with TR legal requirements.

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