Extract eventhub out of pipelines_table

What does this MR do and why?

In preparation for the apollo migration in the pipelines_table, we extract all of the eventhub logic and instead rely on native Vue events. The parents component, the commit_pipelines_table_wrapper and pipelines are now in charge of mapping these events to the appropriate actions (eventhub, mixins, pipeline_store, etc). That way, once we introduce the new graphQL component, we can either address these directly within the pipelines_table or within the new graphql wrapper.

Screenshots or screen recordings

No changes

How to set up and validate locally

Green pipeline!

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