Added worksheets support to notebook viewer

What does this MR do?

Added worksheets support to notebook viewer. Worksheets aren't actually supported in IPython notebooks anymore but this will help with legacy notebooks.

Also improved a little bit of Ruby based on comments from backend review.

The actual changes to the notebook code are here https://gitlab.com/gitlab-org/notebooklab/commit/b448891cca1843006394faa9a2b7e86335bc16e6

assigned to @jschatz1

approved this merge request

enabled an automatic merge when the pipeline for 1db91cd0 succeeds

added 103 commits

• 1db91cd0...91f43587 - 102 commits from branch master
• c71831e8 - Added worksheets support to notebook viewer

Compare with previous version

@iamphill this is failing.

assigned to @iamphill

@jschatz1 its known at the moment, see #30236 (closed)

Known failures. Unrelated. Will merge.

approved this merge request

merged

mentioned in commit ecfbfbf4