Add support for viewing Pending CI jobs
Problem to solve
The "For current branch" sidebar now allows for opening a CI job by left-clicking an item in the tree view. If a log is available, it will show in the editor window.
Currently, jobs in a "Pending" or "Skipped" status do nothing when clicked. Canceled jobs will only do something if the job was underway when it was canceled.
Proposal
The GitLab website displays a placeholder when jobs are opened that have no trace available:
The VS Code plugin should display a similar placeholder in the editor, which should automatically change to a Log viewer if the Job status changes.
Further details
There is currently no similar VS Code class we can extend, so this has to be implemented with a WebView. I would suggest making the associated HTML page as lightweight as possible, preferably without using any JavaScript dependencies. A Retry or Cancel button can be implemented as a normal hyperlink, which executes a Command within VS Code.
Links / references
Part of #423 (closed)
Earlier discussion: !661 (comment 1119085297)