Replace Value Streams Dashboard REST api with graphql

What does this MR do and why?

This MR default enables the vsd_graphql_dora_and_flow_metrics feature flag

Replaces the REST api requests made on the value streams dashboard with requests to graphql endpoints

Screenshots or screen recordings

No visual changes

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 #409499 (closed)