Update kuberlr to 0.6.0 to support dynamic ENV based configs

[mallardduck]

Specifically this will benefit the ability for other teams to be able to reuse this image. In theory any single version of rancher (not within an airgap; i.e. with access to the internet) could toggle allow download using ENV vars and the image would be "universal" to any version of Rancher.

This is not how we are developing and releasing the image due to our "support air-gap by default" mentality. However the new kuberlr feature opens lots of cool new possibilities like that.

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This is related to:

• feat: Use default AllowDownload = true config #42
• Feature request: Add --allow-download flag and its corresponding Viper env var flavio/kuberlr#153
• feat: Support environment variables for config settings flavio/kuberlr#181
• https://github.com/flavio/kuberlr/releases/tag/v0.6.0

[mallardduck]

Essentially this will be fixed by:

• Updating to 0.6.0+ of kuberlr,
• Verifying the ENVs can be set to allow download