Update sample tests to use `rad credential register azure sp` #2822

Job	Run time
Sample tests (demo, ubuntu-latest, true, demo, default, ./samples/demo/app.bicep, --application d...	4m 25s
Sample tests (dapr, ubuntu-latest-m, true, dapr, default, ./samples/dapr/dapr.bicep, -p frontendI...	3m 30s
Sample tests (volumes, ubuntu-latest, true, myapp, default, ./samples/volumes/app.bicep, -p image...	1m 47s
Sample tests (eshop-containers, ubuntu-latest-m, true, eshop, default, ./samples/eshop/eshop.bice...	5m 17s
Sample tests (eshop-azure, ubuntu-latest-m, false, eshop, azure, ./samples/eshop/eshop.bicep, tes...	2s
Sample tests (eshop-aws, ubuntu-latest-m, false, eshop, aws, ./samples/eshop/eshop.bicep, tests/e...	3s
	15m 4s

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