Investigate seq reads on `spam_logs` table on the primary

Observation: There are at times 10k tuples fetched per second (through sequential scans) on spam_logs on the database primary (which is about 3.2GB in size).

https://thanos.gitlab.net/graph?g0.range_input=6h&g0.max_source_resolution=0s&g0.expr=sum(rate(pg_stat_user_tables_seq_tup_read%7Benvironment%3D%22gprd%22%2C%20relname%3D%22spam_logs%22%7D%5B1h%5D))%20by%20(instance)&g0.tab=0&g1.range_input=1h&g1.max_source_resolution=0s&g1.expr=sum(rate(pg_stat_user_tables_idx_tup_fetch%7Benvironment%3D%22gprd%22%2C%20instance%3D%22patroni-03-db-gprd.c.gitlab-production.internal%3A9187%22%2C%20relname%3D%22spam_logs%22%7D%5B1h%5D))%20&g1.tab=0&g2.range_input=1h&g2.max_source_resolution=0s&g2.expr=pg_stat_user_tables_idx_tup&g2.tab=0