Productivity Analytics: Add setInitialData action

What does this MR do?

This MR introduces the following changes to Productivity Analytics app.

• setEndpoint is being invoked now in index.js when we create the root component.
• A new action setInitialData is being introduced which ensures to update the store with the necessary data:
  • For now, this simply sets the default values for startDate and endDate on the store. Later on, additional data will be added which is being passed from BE to FE via data- attributes, see !21031 (merged)

It is a predecessor MR so that deep links can easily be added in !21390 (merged)

Screenshots

N/A

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team