Support pipeline::expedited label

What does this merge request do and why?

This MR adds support for the pipelineexpedited label, which—if applied—will skip building the verify image and all jobs in the verify stage.

Right now, MR pipelines of code changes take over 1 hour to complete, so this change serves two purposes:

1. As self-service for contributors to add pipelineexpedited to avoid wasting computation resources during early development and receive faster feedback. (See the original comment as an example for this, so we don’t have to comment out jobs in the CI config: !3821 (comment 1995363581))
2. To speed up merges in case of reverts but still have a passing pipeline, similar to the master:broken process in gitlab-org/gitlab>, allowing us to iterate faster and ease making two-way-door decisions.

Note: #2143 (closed) suggests to still run a full pipeline on merge trains but considering the second purpose (quote-unquote master:broken within gitlab-org/gitlab-development-kit>) above, maintainers can remove the pipelineexpedited before starting a merge train.

Closes #2143 (closed)

How to set up and validate locally

• Standard pipeline: https://gitlab.com/gitlab-org/gitlab-development-kit/-/pipelines/1370162905
• pipelineexpedited pipeline: https://gitlab.com/gitlab-org/gitlab-development-kit/-/pipelines/1370162905

Impacted categories

The following categories relate to this merge request:

• gdk-reliability - e.g. When a GDK action fails to complete.
• gdk-usability - e.g. Improvements or suggestions around how the GDK functions.
• gdk-performance - e.g. When a GDK action is slow or times out.

Merge request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise an issue to follow-up.
• Documentation added/updated, if needed.
• Announcement added, if change is notable.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.