Resolve "Productivity Analytics: Show error message when there is no data instead of empty charts"

What does this MR do?

This MR changes the loading order/behavior on the Productivity Analytics page. We now fetch data for the main chart first. If successful, we load the remaining charts and the MR table. If the main chart doesn't have any data, we know that the other charts won't have any data either (because they depend on the first chart) Thus, we display a message to the user that no data is available.

Later on, can replace the message with a no data illustration.

We will use the same loading order when the user changes any of the global filters, e.g., group, project, author, milestone, label or timeframe.

This is behind the productivity_analytics feature flag.

Screenshots

Before	After
	productivity_analytics_loading_behavior

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance 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

Closes #32065 (closed)