Cleaned up metars some, fixed humidity calculation

api/migrations/10232024_initial.sql

@@ -52,7 +52,8 @@ CREATE TABLE IF NOT EXISTS metars (
     icao TEXT NOT NULL,
     observation_time TIMESTAMPTZ NOT NULL,
     raw_text TEXT NOT NULL,
-    data JSONB NOT NULL
+    data JSONB NOT NULL,
+    PRIMARY KEY(icao, observation_time)
 );
 
 CREATE INDEX ON metars (observation_time DESC);