Add ValueStreamStageMetrics.projectIds GraphQL query param

What does this MR do and why?

In the process of converting the Value stream analytics charts to GraphQL (!180607 (closed)), I noticed that we don't have the ability to filter by project IDs on the group level. Since the resolver shares the same data fetching logic as the REST api, I simply added the new resolver param to make it accessible to the frontend:

References

#498181 (closed)

MR acceptance checklist

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How to set up and validate locally

1. Seed VSA data

FILTER=customizable_cycle_analytics SEED_CUSTOMIZABLE_CYCLE_ANALYTICS=1 bundle exec rake db:seed_fu

2. Create an extra project in the test group that is created from the data seeder
3. Run GraphQL requests scoped to either project and ensure you receive the expected data. Sample request:

{
  group(fullPath: "flightjs") {
    id
    valueStreams {
      nodes {
        stages(id: "gid://gitlab/Analytics::CycleAnalytics::Stage/19") {
          id
          name
          metrics(
            projectIds: ["gid://gitlab/Project/7", "gid://gitlab/Project/24"]
            timeframe: {
              start: "2024-11-01",
              end: "2025-01-31"
            }
          ) {
            series {
              averageDurations {
                date
                value
              }
            }
          }
        }
      }
    }
  }
}

Related to #498181 (closed)