api/v2/templates/apply isn't clear that template and templates are mutually exclusive

Steps to reproduce:
List the minimal actions needed to reproduce the behavior.

1. Pass the following in a request body to `/api/v2/templates/apply:
   • template property with a Template object.
   • templates property with an array of Template objects.
2. In Template objects for each property, include a resource with the same kind--for example, two resources with "kind": "Label":

  curl -v "${INFLUX_URL}/api/v2/templates/apply" \
    --header "Authorization: Token ${INFLUX_ALL_ACCESS_TOKEN}" \
    --data @- << EOF
    { "orgID": "$INFLUX_ORG_ID",
      "dryRun": true,
      "templates": [
        { "contents": [{
            "apiVersion": "influxdata.com/v2alpha1",
            "kind": "Label",
            "metadata": {
              "name": "unruffled-benz-001"
            },
            "spec": {
              "color": "#326BBA",
              "name": "inputs.cpu"
            }
          }]
        }
      ],
      "template": {
        "contents": [
          {
            "apiVersion": "influxdata.com/v2alpha1",
            "kind": "Bucket",
            "metadata": {
              "name": "heuristic-sinoussi-004"
            },
            "spec": {
              "name": "docker",
              "retentionRules": [
                {
                  "everySeconds": 604800,
                  "type": "expire"
                }
              ]
            }
          },
          {
            "apiVersion": "influxdata.com/v2alpha1",
            "kind": "Label",
            "metadata": {
              "name": "unruffled-benz-004"
            },
            "spec": {
              "color": "#326BBA",
              "name": "inputs.cpu"
            }
          }
        ]
      }  
    }
EOF

Expected behavior:
I expect the error reason to report that template and templates aren't allowed together in the request.

Actual behavior:
Instead, the error reason reports a duplicate name for one of the resources:

       "errors": [
                {
                        "kind": "Label",
                        "fields": [
                                "root",
                                "spec",
                                "name"
                        ],
                        "idxs": [
                                2,
                                null,
                                null
                        ],
                        "reason": "duplicate name: unruffled-benz-004"
                }
        ],
        "code": "unprocessable entity",
        "message": "unprocessable entity"

Environment info:

• System info: Darwin 21.6.0 x86_64
• InfluxDB version: InfluxDB 2.3.0 (git: 090f681737) build_date: 2022-06-16T18:48:06Z

Config:
Copy any non-default config values here or attach the full config as a gist or file.

Logs:
Include snippet of errors in log.

Performance:
Generate profiles with the following commands for bugs related to performance, locking, out of memory (OOM), etc.

# Commands should be run when the bug is actively happening.
# Note: This command will run for ~30 seconds.
curl -o profiles.tar.gz "http://localhost:8086/debug/pprof/all?cpu=30s"
iostat -xd 1 30 > iostat.txt
# Attach the `profiles.tar.gz` and `iostat.txt` output files.

Start at the /api/v2/templates/apply request handling and validation path, using the provided curl body to reproduce the behavior. Verify that supplying both template and templates produces an error stating they are mutually exclusive, rather than a duplicate-resource error.