test: memory consumption on big arrays

[steve-chavez]

~500MB. This caused PostgREST to hit the OOM killer at ~12GB.

That is unexpected, we have these tests:

postgrest/test/memory/memory-tests.sh

Lines 105 to 119 in 4348cb2

	jsonKeyTest "1M" "POST" "/rpc/leak?columns=blob" "27M"
	jsonKeyTest "1M" "POST" "/leak?columns=blob" "21M"
	jsonKeyTest "1M" "PATCH" "/leak?id=eq.1&columns=blob" "21M"
	jsonKeyTest "10M" "POST" "/rpc/leak?columns=blob" "32M"
	jsonKeyTest "10M" "POST" "/leak?columns=blob" "32M"
	jsonKeyTest "10M" "PATCH" "/leak?id=eq.1&columns=blob" "32M"
	jsonKeyTest "50M" "POST" "/rpc/leak?columns=blob" "72M"
	jsonKeyTest "50M" "POST" "/leak?columns=blob" "72M"
	jsonKeyTest "50M" "PATCH" "/leak?id=eq.1&columns=blob" "72M"
	postJsonArrayTest "1000" "/perf_articles?columns=id,body" "20M"
	postJsonArrayTest "10000" "/perf_articles?columns=id,body" "20M"
	postJsonArrayTest "100000" "/perf_articles?columns=id,body" "24M"

So that means a 50MB JSON should consume at most 72 MB RAM and so on. I thought the memory consumed decreased as the payload size increased.

Maybe we need to do similar tests with different MB sizes of arrays, instead of just one big json object (which is what we do on jsonKeyTest).

Originally posted by @steve-chavez in #3954

[steve-chavez]

Maybe try to lower the memory usage upper bound of PATCH requests, see https://github.com/PostgREST/postgrest/pull/4023/files#r2051465105