Add ability to install K3s PR Artifact from GitHub #6737

Job	Run time
build / Build	6m 23s
Integration Tests (certrotation)	2m 1s
Integration Tests (etcdrestore)	1m 45s
Integration Tests (localstorage)	1m 26s
Integration Tests (startup)	6m 24s
Integration Tests (custometcdargs)	43s
Integration Tests (etcdsnapshot)	7m 32s
Integration Tests (kubeflags)	7m 0s
Integration Tests (longhorn)	3m 5s
Integration Tests (secretsencryption)	2m 14s
	38m 33s

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