VSA - Stage Events enhancement
### Overview Value stream stage represents an event pair (start and end events) with additional metadata, such as the name of the stage. Approach - leverage platform events and labels as the underlying architecture for the VSA stages. ### Feedback issue https://gitlab.com/gitlab-org/gitlab/-/issues/520962+ Related also to [workflow states as first-class objects](https://gitlab.com/gitlab-org/gitlab/-/issues/344136#the-broader-cross-stage-opportunity). Once a [workflow is created(option 2)](https://gitlab.com/gitlab-org/gitlab/-/issues/368290#options), it automatically gets a corresponding VSA report and related collection views (boards, lists, ...) generated.
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