MINOR: mode: add log mode for defaults and backends #440

Job	Run time
HAProxy check commit message	0s
generate-models	1m 27s
generate-specification	43s
golangci-lint	1m 36s
Build	24s
go mod tidy	8s
lint-spec	7s
Tests	2m 52s
e2e on HAProxy (2.1)	42s
e2e on HAProxy (2.2)	39s
e2e on HAProxy (2.3)	39s
e2e on HAProxy (2.4)	42s
e2e on HAProxy (2.5)	40s
e2e on HAProxy (2.6)	43s
e2e on HAProxy (2.7)	43s
e2e on HAProxy (2.8)	40s
	12m 45s

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