sqldb: simplify and fixup the existing invoice store schema and queries

This commit attempts to fix some issues with the invoice store's schema that we
couldn't foresee before the implementation was finished. This is safe as the
schema has not been instantiated yet outside of unit tests. Furthermore the
commit updates invoice store SQL queries according to fixes in the schema as
well as to prepare the higher level implementation in the upcoming commits.

sqldb/sqlc/queries/invoice_events.sql

@@ -1,35 +1,41 @@
--- name: InsertInvoiceEvent :exec
+-- name: OnInvoiceCreated :exec
 INSERT INTO invoice_events (
-    created_at, invoice_id, htlc_id, set_id, event_type, event_metadata
+    added_at, event_type, invoice_id
 ) VALUES (
-    $1, $2, $3, $4, $5, $6
+    $1, 0, $2
 );
 
--- name: SelectInvoiceEvents :many
-SELECT *
-FROM invoice_events
-WHERE (
-    invoice_id = sqlc.narg('invoice_id') OR 
-    sqlc.narg('invoice_id') IS NULL
-) AND (
-    htlc_id = sqlc.narg('htlc_id') OR 
-    sqlc.narg('htlc_id') IS NULL
-) AND (
-    set_id = sqlc.narg('set_id') OR 
-    sqlc.narg('set_id') IS NULL
-) AND (
-    event_type = sqlc.narg('event_type') OR 
-    sqlc.narg('event_type') IS NULL
-) AND (
-    created_at >= sqlc.narg('created_after') OR 
-    sqlc.narg('created_after') IS NULL
-) AND (
-    created_at <= sqlc.narg('created_before') OR 
-    sqlc.narg('created_before') IS NULL
-) 
-LIMIT @num_limit OFFSET @num_offset;
+-- name: OnInvoiceCanceled :exec
+INSERT INTO invoice_events (
+    added_at, event_type, invoice_id
+) VALUES (
+    $1, 1, $2
+);
 
--- name: DeleteInvoiceEvents :exec
-DELETE
-FROM invoice_events
-WHERE invoice_id = $1;
+-- name: OnInvoiceSettled :exec
+INSERT INTO invoice_events (
+    added_at, event_type, invoice_id
+) VALUES (
+    $1, 2, $2
+);
+
+-- name: OnAMPSubInvoiceCreated :exec
+INSERT INTO invoice_events (
+    added_at, event_type, invoice_id, set_id
+) VALUES (
+    $1, 3, $2, $3
+);
+
+-- name: OnAMPSubInvoiceCanceled :exec
+INSERT INTO invoice_events (
+    added_at, event_type, invoice_id, set_id
+) VALUES (
+    $1, 4, $2, $3
+);
+
+-- name: OnAMPSubInvoiceSettled :exec
+INSERT INTO invoice_events (
+    added_at, event_type, invoice_id, set_id
+) VALUES (
+    $1, 5, $2, $3
+);