Add grouping to Command Palette

[janfaracik]

This PR adds grouping to the Command Palette, making it easier to identify what each result is.

There are a range of prebuilt groups, UnclassifiedSearchGroup, JobSearchGroup, ComputerSearchGroup, ViewSearchGroup, and UserSearchGroup. Developers can add custom groups too, for example, Design Library could add a group for its components and patterns.

Groups by default don't have a specific ordering, however, the projects group is configured to always appear first, and the unclassified group is configured to always appear last. Results are then ordered by name.

I've also done some minor tidy up to the interface, making the overlay a little less invasive.

Testing done

• Groups appear as expected

Proposed changelog entries

• Add grouping to Command Palette

Proposed upgrade guidelines

N/A

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@jenkinsci/sig-ux

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[daniel-beck]

Could you open a downstream PR for Folders Plugin using this to demonstrate

Developers can add custom groups too

(Where normal folders are not jobs, but MBPLs might end up jobs?)

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Also, per https://www.jenkins.io/doc/book/glossary/#project-1, please call them "Jobs" and not "Projects".

[janfaracik]

Could you open a downstream PR for Folders Plugin using this to demonstrate

Done, using 'Jobs' as a grouping as an example right now although like you say, they're not jobs. Would 'Item' be a better grouping?

Also, per https://www.jenkins.io/doc/book/glossary/#project-1, please call them "Jobs" and not "Projects".

Done, was going to ask about that. Thanks!

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Any thoughts on renaming "Jobs" to just be "Items" so we can include folders too? They're part of the same list when in a view, so I think it'd make sense to group them when searching too.