Add light sync transactions table

- Foreign key to header instead of block
- Can use same Transaction struct for both

db/migrations/00025_create_light_sync_transactions_table.sql

@@ -0,0 +1,14 @@
+-- +goose Up
+CREATE TABLE light_sync_transactions (
+  id        SERIAL PRIMARY KEY,
+  header_id INTEGER NOT NULL REFERENCES headers(id) ON DELETE CASCADE,
+  hash      TEXT,
+  raw       JSONB,
+  tx_index  INTEGER,
+  tx_from   TEXT,
+  tx_to     TEXT,
+  UNIQUE (header_id, hash)
+);
+
+-- +goose Down
+DROP TABLE light_sync_transactions;