chore: Ignore "CIS-DI-0006" container scan best practice check

CIS-DI-0006 is raised because the resulting image has no HEALTHCHECK instruction.

HEALTHCHECK is not part of the OCI spec, but is very Docker-specific.
And, as commented in [1], Jib has no intention to support it,
unless the core OCI spec supports it.

Plus, Kubernetes makes use of its own Startup / Liveness / Readiness
probes for health checks.

[1] GoogleContainerTools/jib#676 (comment)

.github/containerscan/allowedlist.yaml

@@ -0,0 +1,9 @@
+general:
+  vulnerabilities: []
+  bestPracticeViolations:
+    # CIS-DI-0006 : "not found HEALTHCHECK statement"
+    # HEALTHCHECK is not part of the OCI spec, but Docker-specific.
+    # And Jib has no intention to support it, unless the core OCI spec supports it.
+    # https://github.com/GoogleContainerTools/jib/issues/676#issuecomment-442533758
+    # Plus, Kubernetes makes use of its own Startup / Liveness / Readiness probes for health checks.
+    - CIS-DI-0006