Add test functions to neon_test_utils to consume CPU, memory, or local disk.

This is handy for testing VM autoscaling.

test_runner/sql_regress/sql/neon-test-utils.sql

@@ -0,0 +1,15 @@
+-- Test the test utils in pgxn/neon_test_utils. We don't test that
+-- these actually consume resources like they should - that would be
+-- tricky - but at least we check that they don't crash.
+
+CREATE EXTENSION neon_test_utils;
+
+select test_consume_cpu(1);
+
+select test_consume_memory(20); -- Allocate 20 MB
+select test_release_memory(5);  -- Release 5 MB
+select test_release_memory();   -- Release the remaining 15 MB
+
+select test_consume_disk_space(20); -- Allocate 20 MB of disk space
+select test_release_disk_space(5);  -- Release 5 MB
+select test_release_disk_space();   -- Release the remaining 15 MB