Value Stream Analytics - Move duration chart to separate module

Summary

This issue is part of &2434 (closed) and covers separating the Value Stream Analytics 'Duration chart' into a separate module. This follows the pattern used for Productivity Analytics.

• Expose a single component that will be rendered in the base.vue component
• Move [vuex state actions/mutations into separate modules]
• Move relevant tests into a new files
• Add additional tests for each component

Improvements

As the features in Value Stream Analytics have grown, we have continued to add more endpoints, components, and functionality. We are now in a position where it makes sense to split some of the features into separate modules, particularly to help reduce the complexity of the analytics/cycle_analytics/components/base.vue component and the relevant Vuex state.

Risks

• Merge conflicts while changes are happening