refactor: remove SalesInvoiceItemsService and update sales invoice handling

- Deleted SalesInvoiceItemsService as it was not implemented.
- Changed variable declaration from `const` to `let` in SalesInvoicesService for sales invoice creation.
- Updated response handling after sending to TSP provider in SalesInvoicesService.
- Renamed payload properties in TspProvider DTOs for clarity.
- Enhanced error handling in SalesInvoiceTspSwitchService for unsupported providers.
- Refactored SalesInvoiceTspService to utilize utility functions for payload building and sending.
- Updated PrismaService to increase connection limit and utilize dynamic options.
- Added new migration scripts to update database schema for sale_invoice_tsp_attempts.
- Introduced utility functions for building payloads and handling responses in sales invoice processing.

src/generated/prisma/internal/prismaNamespace.ts

@@ -4073,8 +4073,9 @@ export const SaleInvoiceTspAttemptsScalarFieldEnum = {
   id: 'id',
   attempt_no: 'attempt_no',
   status: 'status',
-  request_payload: 'request_payload',
-  response_payload: 'response_payload',
+  raw_request_payload: 'raw_request_payload',
+  provider_request_payload: 'provider_request_payload',
+  provider_response_payload: 'provider_response_payload',
   message: 'message',
   sent_at: 'sent_at',
   received_at: 'received_at',