Update the Helm chart to include WireMock 3.0.0 and use the official image

[oleg-nenashev]

Addresses #22 and #25

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• Test coverage that demonstrates that the change works as expected
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[oleg-nenashev]

 Warning  Unhealthy  4m30s (x3 over 4m50s)  kubelet            Liveness probe failed: Get "http://10.244.0.2:9021/__admin/webapp": dial tcp 10.244.0.2:9021: connect: connection refused