Set default effective_io_concurrency to 256

Since all drives are SSDs in arrays with at least two drives, 256
is a reasonable default. NVMe drives could have this set even higher,
but this is a reasonable start.

cookbooks/postgresql/attributes/default.rb

@@ -9,7 +9,7 @@
 default[:postgresql][:settings][:defaults][:work_mem] = "4MB"
 default[:postgresql][:settings][:defaults][:maintenance_work_mem] = "64MB"
 default[:postgresql][:settings][:defaults][:max_stack_depth] = "2MB"
-default[:postgresql][:settings][:defaults][:effective_io_concurrency] = "1"
+default[:postgresql][:settings][:defaults][:effective_io_concurrency] = "256"
 default[:postgresql][:settings][:defaults][:max_worker_processes] = "8"
 default[:postgresql][:settings][:defaults][:max_parallel_workers_per_gather] = "2"
 default[:postgresql][:settings][:defaults][:max_parallel_workers] = "8"