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/scheduler_perf/config/dra/pod-with-claim-ref.yaml

@@ -11,6 +11,5 @@ spec:
       - name: resource
   resourceClaims:
   - name: resource
-    source:
-      # Five pods share access to the same claim.
-      resourceClaimName: test-claim-{{div .Index 5}}
+    # Five pods share access to the same claim.
+    resourceClaimName: test-claim-{{div .Index 5}}

test/integration/scheduler_perf/config/dra/pod-with-claim-template.yaml

@@ -11,5 +11,4 @@ spec:
       - name: resource
   resourceClaims:
   - name: resource
-    source:
-      resourceClaimTemplateName: test-claim-template
+    resourceClaimTemplateName: test-claim-template

test/integration/scheduler_perf/config/dra/pod-with-many-claim-templates.yaml

@@ -14,14 +14,10 @@ spec:
       - name: resource-2b
   resourceClaims:
   - name: resource-1a
-    source:
-      resourceClaimTemplateName: test-claim-template
+    resourceClaimTemplateName: test-claim-template
   - name: resource-1b
-    source:
-      resourceClaimTemplateName: test-claim-template
+    resourceClaimTemplateName: test-claim-template
   - name: resource-2a
-    source:
-      resourceClaimTemplateName: another-test-claim-template
+    resourceClaimTemplateName: another-test-claim-template
   - name: resource-2b
-    source:
-      resourceClaimTemplateName: another-test-claim-template
+    resourceClaimTemplateName: another-test-claim-template