MGMT-16452: Change MCE subscription to use the default channel

[eifrach]

List all the issues related to this PR

• New Feature
• Enhancement
• Bug fix
• Tests
• Documentation
• CI/CD

What environments does this code impact?

• Automation (CI, tools, etc)
• Cloud
• Operator Managed Deployments
• None

How was this code tested?

• assisted-test-infra environment
• dev-scripts environment
• Reviewer's test appreciated
• Waiting for CI to do a full test run
• Manual (Elaborate on how it was tested)
• No tests needed

Checklist

• Title and description added to both, commit and PR.
• Relevant issues have been associated (see CONTRIBUTING guide)
• This change does not require a documentation update (docstring, docs, README, etc)
• Does this change include unit-tests (note that code changes require unit-tests)

Reviewers Checklist

• Are the title and description (in both PR and commit) meaningful and clear?
• Is there a bug required (and linked) for this change?
• Should this PR be backported?

[danmanor]

/test