Add loading indicator to the test liveview

[r-richardson]

This PR removes the empty box which was visible in the webui before liveview content is received by the responsible canvas element. It also adds a loading animation indicating to the user that the liveview is still being loaded.

Related Issue: https://progress.opensuse.org/issues/134840

[kalikiana]

[15:22:13] t/full-stack.t ......... 31/? Bailout called.  Further testing stopped:  test 't/full-stack.t' exceeds runtime limit of '1800' seconds
FAILED--Further testing stopped: test 't/full-stack.t' exceeds runtime limit of '1800' seconds

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 98.98%. Comparing base (c53c994) to head (012ceaf). Report is 6 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6023   +/-   ##
=======================================
  Coverage   98.98%   98.98%           
=======================================
  Files         395      395           
  Lines       39382    39405   +23     
=======================================
+ Hits        38982    39005   +23     
  Misses        400      400           

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[mergify[bot]]

This pull request is now in conflicts. Could you fix it? 🙏

[github-actions[bot]]

Great PR! Please pay attention to the following items before merging:

Files matching assets/stylesheets/**:

• [ ] Consider providing screenshots in a PR comment to show the difference visually

This is an automatically generated QA checklist based on modified files.