CLOUDP-364442 - remove om6 testing infra

[nammn]

Summary

• This PR drops om6 testing infra from evg
• OM6 is EOL since January 31, 2025
• OM6 support has officially been dropped since 1.31.x

Proof of Work

• green patch without om6 (normal patches):
• manually you can still trigger om6: patch

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 1.6.1 Release Notes

Bug Fixes

• Backed up the agent password in a secret for SCRAM authentication to prevent unnecessary password rotations.
• MongoDB Adding missing ownerrefs to ensure proper resource deletion by kubernetes.
• Single Cluster Deleting resources created by CRD now only happens on multi-cluster deployments. Single Cluster will solely rely on ownerrefs.
• MongoDB, MongoDBOpsManager: Improve validation for featureCompatibilityVersion field in MongoDB and MongoDBOpsManager spec.
  The field now enforces proper semantic versioning. Previously, invalid semver values could be accepted,
  potentially resulting in incorrect configurations.
• Roles configured via Ops Manager UI or API will no longer be removed by the operator

Other Changes

• Future releases will include a new asset, release_info_.json, which provides detailed information about each MongoDB Controllers for Kubernetes release, including a clear list of all container images. This will help customers, especially those running in air-gapped environments, easily identify all required images for a given release.

[mircea-cosbuc]

LGTM! Nice to see this cleanup.