Install gcloud auth plugin in kanister build image #7180

Job	Run time
gomod	56s
docs	31s
image_tags	1s
build (controller)	2m 28s
build (kanctl)	2m 31s
build (kando)	2m 21s
reno_lint	42s
lint	3m 36s
test (test)	11m 13s
test (integration-test)	8m 4s
test (helm-test)	3m 16s
release	0s
release_example_docker_images	0s
	35m 39s

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