opensearch output: action does not support "create"

Description

The output opensearch action does not support create, as a result can not sink messages into index of datastream type in opensearch

Location

The supportted action is in internal/impl/opensearch/output.go

Test

Preparation

Opensearch: 3.6.0
Kafka: 4.0.0
Redpandadata/connect: 4.90.3

Create events as a datastream in opensearch

Configure connector output

output_resources:
  - label: o_kafka_os
    broker:
      pattern: greedy
      copies: 5
      outputs:
        - drop_on:
            error_patterns:
              - illegal_argument_exception
              - Compressor detection
              - invalid json
            output:
              opensearch:
                urls: [ "${OS_URI}" ]
                action: index
                index: 'events'
                id: '${! uuid_v4() }'

Result

Input data in kafka, and then redpanda-connect will has following error in log:

time="2026-06-15T02:44:20Z" level=error msg="Failed to send message to opensearch: illegal_argument_exception: only write ops with an op_type of create are allowed in data streams" @service=redpanda-connect  label="" path=root.output_resources.broker.outputs.0.drop_on.output
time="2026-06-15T02:44:20Z" level=warning msg="Message dropped due to error matching pattern 0: illegal_argument_exception: only write ops with an op_type of create are allowed in data streams" @service=redpanda-connect label="" path=root.output_resources.broker.outputs.0

Proposal

Add the following code into internal/impl/opensearch/output.go, just like elasticsearch_v9

	case "index":
		r = &opensearchutil.BulkIndexerItem{
			Index:  p.Index,
			Action: "index",
			Body:   bytes.NewReader(p.Payload),
		}
		if p.ID != "" {
			r.DocumentID = p.ID
		}
		if p.Routing != "" {
			r.Routing = &p.Routing
		}
+	case "create":
+		r = &opensearchutil.BulkIndexerItem{
+			Index:  p.Index,
+			Action: "create",
+			Body:   bytes.NewReader(p.Payload),
+		}
+		if p.ID != "" {
+			r.DocumentID = p.ID
+		}
+		if p.Routing != "" {
+			r.Routing = &p.Routing
+		}

Then can set the action to "create", then can write data into a index of datastream in opensearch

Start in internal/impl/opensearch/output.go and compare the existing action handling with the analogous elasticsearch_v9 implementation mentioned in the issue. Add support for configuring the OpenSearch action as "create", preserving the documented index, ID, and routing behavior. Done means messages can be written to an OpenSearch data stream without the op_type error.