Update che-docs preview to use https instead of http

[dkwon17]

Is your enhancement related to a problem? Please describe

When running the start-preview-server task to start the che-docs preview server, the preview is accessible by clicking the Open in New Tab button in the notification that appears:

The preview url only works with http, not https.

Describe the solution you'd like

It would be better if it was using https.

I noticed that simply changing the protocol to https like so: dkwon17/che-docs@b2a9df1 did not fix the problem, as I see this message when trying to access the preview url:

Describe alternatives you've considered

No response

Additional context

No response

[ibuziuk]

@dkwon17 seems to work for me with eclipse-che/che-docs#2700