Show six months of data on the Value Streams Dashboard

What does this MR do and why?

Updates the Value Streams Dashboard to use the same underlying panel visualization used by the AI impact dashboard, doubling the time window visible in the metric tables.

Feature tests were updated to use regex to validate the table rows, as opposed to exact data matching. The previous test structure has caused recurring flakey test issues which should now be fixed moving forward

Docs for the Value Streams Dashboard also needed to be significantly updated to account for the changes between the old and new table structures.

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

• Navigate to the Value streams dashboard for any group/project: Analyze > Analytics dashboards > Value Streams Dashboard
• Verify that the metric tables load correctly with the 6-month layout

MR acceptance checklist

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

Related to #541489