install buildx with docker driver #355

Job	Run time
prepare_pgversion_matrix	3s
push-test-images-for-dev (citusupgradetester)	3m 41s
push-test-images-for-dev (pgupgradetester)	2m 26s
push-test-images-for-release	0s
push-test-images-for-dev (stylechecker)	2m 34s
push-test-images-for-dev (extbuilder, 14.15)	1m 34s
push-test-images-for-dev (extbuilder, 15.10)	1m 40s
push-test-images-for-dev (extbuilder, 16.6)	1m 28s
push-test-images-for-dev (extbuilder, 17.2)	1m 31s
push-test-images-for-dev (exttester, 14.15)	3m 47s
push-test-images-for-dev (exttester, 15.10)	4m 54s
push-test-images-for-dev (exttester, 16.6)	3m 43s
push-test-images-for-dev (exttester, 17.2)	4m 8s
push-test-images-for-dev (failtester, 14.15)	1m 59s
push-test-images-for-dev (failtester, 15.10)	2m 19s
push-test-images-for-dev (failtester, 16.6)	1m 58s
push-test-images-for-dev (failtester, 17.2)	2m 38s
	40m 23s

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