Fixing freezing dockerfile create page

[ReinierCC]

This PR is to fix the following issue:

where the "Automated Deployments: Draft a Dockerfile" page would freeze for any user input after clicking the create button.

This occured because the draft command being executed to create the dockerfile was waiting for cli style user input about the BUILDVERSION.

Previously the builderImageTag was or'ed with an empty string. But builderImageTag was already of type string | null .

By removing the empty string, the draft binary uses BUILDERTAG as null and does not request user input.

There still exists issue #944 for python dockerfiles. But the fix for that would best come from a modification to the draft binary itself.

[ReinierCC]

VSIX For Testing (Remove .zip from file name):

vscode-aks-tools-1.4.9-docker-create-freeze-fix.vsix.zip