Enable mistakenly disabled image signing + conform to new cosign version

[MaciejKaras]

Summary

Image signing was disabled globally by mistake. This change fixes the issue while adjusting to the new cosign version.

Proof of Work

On staging we now successfully signs images -> https://evergreen.mongodb.com/version/6903557435b1f60007ee8cfa?redirect_spruce_users=true

[2025/10/30 13:23:52.472] Login Succeeded [2025/10/30 13:23:52.472] INFO 2025-10-30 12:23:52,472 [atomic_pipeline] Signing image [2025/10/30 13:23:52.472] DEBUG 2025-10-30 12:23:52,472 [image_signing] Signing image 268558157000.dkr.ecr.us-east-1.amazonaws.com/staging/mongodb-kubernetes-init-appdb:1.6.0-mk [2025/10/30 13:24:17.675] DEBUG 2025-10-30 12:24:17,675 [image_signing] Signing successful [2025/10/30 13:24:17.675] DEBUG 2025-10-30 12:24:17,675 [image_signing] Verifying signature of 268558157000.dkr.ecr.us-east-1.amazonaws.com/staging/mongodb-kubernetes-init-appdb:1.6.0-mk [2025/10/30 13:24:21.009] DEBUG 2025-10-30 12:24:18,491 [image_signing] Successful verification [2025/10/30 13:24:21.009] Finished command 'subprocess.exec' in function 'pipeline' (step 3 of 3) in 5m3.441945822s. 

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
  • refer to Changelog files and Release Notes section in CONTRIBUTING.md for more details

[github-actions]

⚠️ (this preview might not be accurate if the PR is not rebased on current master branch)

MCK 1.6.0 Release Notes

New Features

• MongoDBCommunity: Added support to configure custom cluster domain via newly introduced spec.clusterDomain resource field. If spec.clusterDomain is not set, environment variable CLUSTER_DOMAIN is used as cluster domain. If the environment variable CLUSTER_DOMAIN is also not set, operator falls back to cluster.local as default cluster domain.
• Helm Chart: Introduced two new helm fields operator.podSecurityContext and operator.securityContext that can be used to configure securityContext for Operator deployment through Helm Chart.

Bug Fixes

• Fixed parsing of the customEnvVars Helm value when values contain = characters.
• ReplicaSet: Blocked disabling TLS and changing member count simultaneously. These operations must now be applied separately to prevent configuration inconsistencies.

Other Changes

• kubectl-mongodb plugin: cosign, the signing tool that is used to sign kubectl-mongodb plugin binaries, has been updated to version 3.0.2. With this change, released binaries will be bundled with .bundle files containing both signature and certificate information. For more information on how to verify signatures using new cosign version please refer to -> https://github.com/sigstore/cosign/blob/v3.0.2/doc/cosign_verify-blob.md

[MaciejKaras]

sign was always set and it was overriding the value from build_info.json:

sign = args.sign if args.sign is not None else image_build_info.sign