fix(coordinator): Add unique_end_date constraint to funding_rates

We only need one funding rate entry per `end_date`.

Without this change we were getting a new duplicate entry per
maker restart.

We `DO NOTHING` on conflict to ensure that the actually new rows in
the batch will be inserted if we encounter any conflicts.

coordinator/migrations/2024-06-06-045129_add_unique_end_date_constraint/down.sql

@@ -0,0 +1,2 @@
+ALTER TABLE funding_rates
+DROP CONSTRAINT IF EXISTS unique_end_date;

coordinator/migrations/2024-06-06-045129_add_unique_end_date_constraint/up.sql

@@ -0,0 +1,2 @@
+ALTER TABLE funding_rates
+ADD CONSTRAINT unique_end_date UNIQUE (end_date);

coordinator/src/funding_fee/db/funding_rates.rs

@@ -39,6 +39,8 @@ pub fn insert_funding_rates(
 
     let affected_rows = diesel::insert_into(funding_rates::table)
         .values(funding_rates)
+        .on_conflict(funding_rates::end_date)
+        .do_nothing()
         .execute(conn)?;
 
     if affected_rows == 0 {