ci: add Many NodePools focus row to kind-perf-e2e matrix

Wires the new Many NodePools performance spec into the kind-perf-e2e
workflow so the DescribeTable sweep runs alongside the other scenarios
on every push to main. Focus regex matches the Ginkgo Context in
many_nodepools_test.go.

Fan-out cost is one additional matrix row against the existing seven
scenarios. If the largest sweep entry (500 NodePools) overflows the
per-matrix-job wall clock on the first run, splitting the DescribeTable
into two Its and adding a second matrix row is the mitigation path.

Signed-off-by: Nathaniel Jones <jonesflp@amazon.com>

Author: nathangeology

.github/workflows/kind-perf-e2e.yaml

@@ -31,6 +31,8 @@ jobs:
             focus: "Do Not Disrupt Performance Test"
           - name: "Self Anti-Affinity Deployment Interference"
             focus: "Self Anti-Affinity Deployment Interference"
+          - name: "Many NodePools"
+            focus: "Many NodePools"
     uses: ./.github/workflows/e2e.yaml
     with:
       suite: Performance