feat(tax): add endpoints to create tax regions and tax rates (#6533)

**What**
Adds:
- POST /admin/tax-regions
- POST /admin/tax-rates
- GET /admin/tax-rates
- `createTaxRegionsWorkflow`
- `createTaxRatesWorkflow`

packages/tax/src/services/tax-module-service.ts

@@ -148,7 +148,7 @@ export default class TaxModuleService<
       await this.taxRateRuleService_.create(rulesToCreate, sharedContext)
     }
 
-    return await this.baseRepository_.serialize<TaxTypes.TaxRateDTO>(rates, {
+    return await this.baseRepository_.serialize<TaxTypes.TaxRateDTO[]>(rates, {
       populate: true,
     })
   }