pg qrep: avro schema nullable by default

[serprex]

alternative to #3613

[codecov]

❌ 2 Tests Failed:

Tests completed	Failed	Passed	Skipped
1508	2	1506	136

View the top 2 failed test(s) by shortest run time

github.com/PeerDB-io/peerdb/flow/e2e::Test_PubSub

Stack Traces | 0s run time

=== RUN   Test_PubSub
=== PAUSE Test_PubSub
=== CONT  Test_PubSub
--- FAIL: Test_PubSub (0.00s)

github.com/PeerDB-io/peerdb/flow/e2e::Test_PubSub/TestInitialLoad

Stack Traces | 71.5s run time

=== RUN   Test_PubSub/TestInitialLoad
=== PAUSE Test_PubSub/TestInitialLoad
=== CONT  Test_PubSub/TestInitialLoad
    pubsub_test.go:300: 
        	Error Trace:	.../flow/e2e/pubsub_test.go:300
        	Error:      	Received unexpected error:
        	            	rpc error: code = DeadlineExceeded desc = context deadline exceeded
        	Test:       	Test_PubSub/TestInitialLoad
    pubsub_test.go:105: begin tearing down postgres schema ps_gjpkeu1g
--- FAIL: Test_PubSub/TestInitialLoad (71.49s)

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