Move duration chart vuex to separate module

What does this MR do?

As part of &2434 (closed) we are taking the time to refactor some of the FE code for value stream analytics. This MR follows !28624 (merged) which moved the duration chart into a separate component. Here we are moving the related vuex code into a separate module.

• 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 new files
• Add additional tests for the new duration_chart component
• Replaces done callbacks in specs with promises

Screenshots

No visual changes

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
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

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 #197336 (closed)