Bug 1066272 - Add the possibility to display unscheduled tasks

[JohanLorenzo]

Latest rationale.

Edit 2025-12-03: Color has changed from tan to turquoise.

@Archaeopteryx, r?

[Archaeopteryx]

Thanks. r+ with the top 3 commits from https://github.com/Archaeopteryx/treeherder/commits/jlorenzo-unscheduled/

[JohanLorenzo]

Thank you for your review and the follow-up patches, @Archaeopteryx! I had to rebase my PR against master because of conflicts. I took the liberty of incorporating your commits into the PR (notably the one that changed the color to turquoise). I don't have the permission to merge the PR so I leave it to you, @Archaeopteryx.

[moijes12]

@Archaeopteryx @JohanLorenzo

I am pretty new here so I may be wrong.
The code looks good. However, while going through the backend code, I did observe that we maintain the state in strings and repeat those strings every time we need to compare state or do any operation on it. Since the state is a set of predefined values ("pending", "running", "undefined" etc.), I would recommend that we use Enums or constant classes to store the state. This way we all operation will be performed keeping the enum in mind which might make the code more readable and reduce the change of any bug that might get introduced due to any typo in the string.