sqldb+invoices: add migration to fix incorrectly stored invoice expiries

Previously, when using the native schema, invoice expiries were incorrectly
stored as 64-bit values (expiry in nanoseconds instead of seconds), causing
overflow issues. Since we cannot determine the original values, we will set
the expiries for existing invoices to 1 hour with this migration.

sqldb/sqlc/migrations/000004_invoice_expiry_fix.down.sql

@@ -0,0 +1,2 @@
+-- Given that all expiries are changed in this migration we won't be able to
+-- roll back to the previous values.

sqldb/sqlc/migrations/000004_invoice_expiry_fix.up.sql

@@ -0,0 +1,14 @@
+-- Update the expiry for all records in the invoices table. This is needed as 
+-- previously we stored raw time.Duration values which are 64 bit integers and
+-- are used to express duration in nanoseconds however the intent is to store
+-- invoice expiry in seconds.
+
+-- Update the expiry to 86400 seconds (24 hours) for non-AMP invoices.
+UPDATE invoices
+SET expiry = 86400
+WHERE is_amp = FALSE;
+
+-- Update the expiry to 2592000 seconds (30 days) for AMP invoices
+UPDATE invoices
+SET expiry = 2592000
+WHERE is_amp = TRUE;