[xy] Interpolate global vars in k8s executor namespace

[wangxiaoyou1993]

Description

Close: #4488

Support dynamic namespace in k8s executor by interpolating vars in the namespace
https://docs.mage.ai/development/variables/overview

How Has This Been Tested?

• Tested with local kubernetes cluster

Checklist

• The PR is tagged with proper labels (bug, enhancement, feature, documentation)
• I have performed a self-review of my own code
• I have added unit tests that prove my fix is effective or that my feature works
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• If new documentation has been added, relative paths have been added to the appropriate section of docs/mint.json

cc: