feat: provide the sha256 digest as an oci_image target #832

Job	Run time
test-auth	2m 41s
matrix-prep-bazelversion	4s
test (ubuntu-latest, 6.2.0, ., true)	3m 43s
test (ubuntu-latest, 6.2.0, ., false)	3m 39s
test (ubuntu-latest, 6.2.0, e2e/custom_registry, false)	49s
test (ubuntu-latest, 6.2.0, e2e/wasm, false)	4m 15s
test (ubuntu-latest, 6.2.0, e2e/smoke, true)	2m 26s
test (ubuntu-latest, 6.2.0, e2e/smoke, false)	3m 29s
test (ubuntu-latest, 6.2.0, e2e/crane_as_registry, true)	2m 21s
test (ubuntu-latest, 6.2.0, e2e/crane_as_registry, false)	3m 28s
test (ubuntu-latest, 5.3.2, ., false)	4m 9s
test (ubuntu-latest, 5.3.2, e2e/custom_registry, false)	1m 2s
test (ubuntu-latest, 5.3.2, e2e/wasm, false)	4m 58s
test (ubuntu-latest, 5.3.2, e2e/smoke, false)	3m 9s
test (ubuntu-latest, 5.3.2, e2e/crane_as_registry, false)	3m 9s
	43m 22s

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