Support policy variable replacement (#7085)

This PR supports iam and bucket policies to have
policy variable replacements in resource and
condition key values.

For example
- ${aws:username}
- ${aws:userid}

pkg/policy/resource_test.go

@@ -124,7 +124,7 @@ func TestResourceMatch(t *testing.T) {
 	}
 
 	for i, testCase := range testCases {
-		result := testCase.resource.Match(testCase.objectName)
+		result := testCase.resource.Match(testCase.objectName, nil)
 
 		if result != testCase.expectedResult {
 			t.Fatalf("case %v: expected: %v, got: %v", i+1, testCase.expectedResult, result)