DRA: remove "source" indirection from v1 Pod API

This makes the API nicer:

    resourceClaims:
    - name: with-template
      resourceClaimTemplateName: test-inline-claim-template
    - name: with-claim
      resourceClaimName: test-shared-claim

Previously, this was:

    resourceClaims:
    - name: with-template
      source:
        resourceClaimTemplateName: test-inline-claim-template
    - name: with-claim
      source:
        resourceClaimName: test-shared-claim

A more long-term benefit is that other, future alternatives
might not make sense under the "source" umbrella.

This is a breaking change. It's justified because DRA is still
alpha and will have several other API breaks in 1.31.

test/integration/auth/node_test.go

@@ -225,8 +225,8 @@ func TestNodeAuthorizer(t *testing.T) {
 						{Name: "pvc", VolumeSource: corev1.VolumeSource{PersistentVolumeClaim: &corev1.PersistentVolumeClaimVolumeSource{ClaimName: "mypvc"}}},
 					},
 					ResourceClaims: []corev1.PodResourceClaim{
-						{Name: "namedclaim", Source: corev1.ClaimSource{ResourceClaimName: pointer.String("mynamedresourceclaim")}},
-						{Name: "templateclaim", Source: corev1.ClaimSource{ResourceClaimTemplateName: pointer.String("myresourceclaimtemplate")}},
+						{Name: "namedclaim", ResourceClaimName: pointer.String("mynamedresourceclaim")},
+						{Name: "templateclaim", ResourceClaimTemplateName: pointer.String("myresourceclaimtemplate")},
 					},
 				},
 			}, metav1.CreateOptions{})