Draft: Apollo MR pipelines - New component for retry and cancel actions

What does this MR do and why?

In app/assets/javascripts/pipelines/components/pipelines_list/pipeline_operations.vue we are adding two GlButton for retry and cancel. We could consolidate these 2 in a single component which will also handle the mutations for retrying and cancelling.

This also mean that this component would handle the modal for confirming the cancel of the pipeline and we could get rid of the eventHub. On top of that, it means that we can keep the state isCancelling local within the same component instead of emitting al the way up and then passing a prop to know if it's being canceled since the action will occur in a child component (the modal).

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Related to #420631 (closed)