Add throughput chart, stats and table stories

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What does this MR do and why?

Closes #428283 (closed)

1. Adds a new story file named throughput_chart.stories.js for the throughput_chart.vue component

   • The default story renders the chart with data
   • A story for the chart without any data available
   • A story for the chart in the loading state

2. Adds a new story file named throughput_table.stories.js for the throughput_table.vue component

   • The default story renders the table with data
   • A story for the table without any data available
   • A story for the chart in the loading state

3. Adds a new story file named throughput_stats.stories.js for the throughput_stats.vue component

   • The default story renders the table with data
   • A story for the stats in the loading state

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Throughput Chart

Default	No Data	Loading

Throughput Table

Default	No Data	Loading

Throughput Stats

Default	Loading

How to set up and validate locally

1. Install storybook - in the terminal run:

yarn storybook:install

2. Start storybook - in the terminal run:

yarn storybook:start

2. Checkout the stories under ee / analytics / merge_request_analytics / components
   • http://localhost:9002/?path=/story/ee-analytics-merge-request-analytics-components-throughput-chart--default