Add voucher functionality

...migrations/20230430160007_add_voucher_table/migration.sql

prisma/schema.prisma

src/lib/customcodes.js

src/routes/+page.svelte

src/routes/admin/+page.svelte

src/routes/admin/api/transactions.js

src/routes/admin/user/[id]/+page.svelte

src/routes/admin/vouchers/+page.server.js

src/routes/admin/vouchers/+page.svelte

src/routes/admin/vouchers/VoucherItem.svelte

src/routes/admin/vouchers/VoucherList.svelte

src/routes/api/[slug]/+server.js

src/routes/api/transactions.js