Fix reset scripts

[Julien-Ben]

Summary

Test runs can leave behind stale state that breaks subsequent runs in two ways:

1. Stale Cloud Manager projects — the operator creates per-resource projects (e.g. mongodb-test-mdb-sh) that aren't cleaned up by the existing delete script. Old automation configs persist and cause cert hash mismatches that deadlock the agent.
2. Istio leftovers — multi-cluster runs label namespaces with istio-injection and create PeerAuthentication resources. When a single-cluster test reuses the same namespace, sidecar injection kicks in unexpectedly.
3. Istio labeling without mTLS — the prepare-multi-cluster script was applying the Istio injection label even when MULTI_CLUSTER_NO_MESH=true, and defaulting to mesh-enabled when the env var was unset (contrary to the original bash behavior).

This PR fixes all three:

• delete_om_projects.sh now finds and deletes projects matching <namespace>-* prefix
• reset/main.go strips the istio-injection label and deletes PeerAuthentication resources during namespace reset
• prepare-multi-cluster/main.go only applies Istio labels when mTLS is actually requested, and defaults MULTI_CLUSTER_NO_MESH to "true" when unset (matching the old bash behavior)

Proof of Work

Verified against local multi-cluster and single-cluster test runs.

Checklist

• Have you linked a jira ticket and/or is the ticket in the title?
• Have you checked whether your jira ticket required DOCSP changes?
• Have you added changelog file?
  • use skip-changelog label if not needed

[github-actions]

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MCK 1.7.1 Release Notes

Other Changes

• Container images: Merged the init-database and init-appdb init container images into a single init-database image. The init-appdb image will no longer be published and does not affect existing deployments.