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.

prisma/schema/shared/sales.prisma

@@ -72,15 +72,16 @@ model SaleInvoiceTspAttempts {
   attempt_no Int
   status     TspProviderResponseStatus
 
-  request_payload  Json?
-  response_payload Json?
-  message          String @db.Text
+  raw_request_payload       Json
+  provider_request_payload  Json?
+  provider_response_payload Json?
+  message                   String @db.Text
 
   sent_at     DateTime? @db.Timestamp(0)
   received_at DateTime? @db.Timestamp(0)
   created_at  DateTime  @default(now()) @db.Timestamp(0)
 
-  invoice_id String       @unique
+  invoice_id String
   invoice    SalesInvoice @relation(fields: [invoice_id], references: [id], onDelete: Cascade)
 
   @@unique([invoice_id, attempt_no])