porch: raise memory limit, also remove CPU limit (#2829)

The memory limit was too tight and we were hitting it (and I don't
think the limit was high enough that we should prioritize the usage -
yet!)

For CPU, the general advice is to set a request but not to set a
limit.

porch/config/deploy/3-porch-server.yaml

@@ -47,11 +47,10 @@ spec:
           imagePullPolicy: Always
           resources:
             requests:
-              memory: "64Mi"
+              memory: "256Mi"
               cpu: "250m"
             limits:
-              memory: "128Mi"
-              cpu: "1000m"
+              memory: "512Mi"
           volumeMounts:
             - mountPath: /cache
               name: cache-volume