Add deployment frequency forecast utils

What does this MR do and why?

This MR refactors the deployment frequency chart component adds some utils in preparation for !125849 (merged):

• Emits the select-chart event when the date range is changed
• Adds the forecastDataToSeries helper to generate the data series for a forecast
• Adds the calculateForecast helper to generate a data forecast
• Adds some additional computed props

Screenshots or screen recordings

No visual changes

How to set up and validate locally

$ yarn jest --watch dora

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #409875 (closed)