Add a shared cargo cache to the rust test pipeline.

This is to be a better citizen by not constantly hammering github for the dependencies.

.lighthouse/pipeline-rust-test.yaml

@@ -106,6 +106,8 @@ spec:
         workspaces:
           - name: source
             workspace: git-source
+          - name: cargo-cache
+            workspace: cargo-cache
         runAfter:
           - build-image
         params:
@@ -163,6 +165,7 @@ spec:
     workspaces:
       - name: git-source
       - name: docker-credentials
+      - name: cargo-cache
   workspaces:
     - name: git-source
       volumeClaimTemplate:
@@ -174,6 +177,9 @@ spec:
             requests:
               storage: 10Gi
       subPath: rust-source
+    - name: cargo-cache
+      persistentVolumeClaim:
+        claimName: cargo-cache
     - name: docker-credentials
       secret:
         secretName: harbor-plain