During message correlation with `resultEnabled`, wrong entity is populated when "resultType": "Execution"

Environment (Required on creation)

REST API 7.21.0+

Description (Required on creation; please attach any relevant screenshots, stacktraces, log files, etc. to the ticket)

Perform message correlation with resultEnabled and expected resultType: Execution The resultType isn't considered, always the processInstance entity is returned.

Steps to reproduce (Required on creation)

Get the example from here: https://jira.camunda.com/browse/SUPPORT-21725?focusedCommentId=347192&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-347192

start the application: mvn spring-boot:run
send request for message correlation to start process instance (expected return type: process defintion)

curl --location 'http://localhost:8080/engine-rest/message' \
--header 'Content-Type: application/json' \
--data '{
    "messageName": "startPM",
    "resultEnabled": true
}'

send another request for message correlation

curl --location 'http://localhost:8080/engine-rest/message' \
--header 'Content-Type: application/json' \
--data '{
    "messageName": "startESP",
    "resultEnabled": true
}'

Observed Behavior (Required on creation)

The response contains resultType: Execution and execution: null.

[
    {
        "resultType": "Execution",
        "execution": null,
        "processInstance": {
            "links": [],
            "id": "aa79036a-06d6-11ef-a3f3-00ff18b69f72",
            "definitionId": "81d0b026-06d6-11ef-a3f3-00ff18b69f72",
            "businessKey": null,
            "caseInstanceId": null,
            "ended": false,
            "suspended": false,
            "tenantId": null
        }
    }
]

Expected behavior (Required on creation)

The response contains resultType: Execution and the execution dto is populated.

[
    {
        "resultType": "Execution",
        "execution": {
            "id": "99e27609-06d9-11ef-a41a-00ff18b69f72",
            "processInstanceId": "99e27609-06d9-11ef-a41a-00ff18b69f72",
            "ended": false,
            "tenantId": null
        },
        "processInstance": null
    }
]

(created with 7.20)

Root Cause (Required on prioritization)

Since 7.21.0 the process instance is populated in the result all the time so it can be used in the user operation logs. The REST API, doesn't consider the returnType but checks if the process instance is present: https://github.com/camunda/camunda-bpm-platform/blob/master/engine-rest/engine-rest/src/main/java/org/camunda/bpm/engine/rest/dto/message/MessageCorrelationResultDto.java#L41-L44 (even thought the execution is also present)

Solution Ideas

In the REST API, populate the process instance/execution dto after considering the resultType.

Hints

Breakdown

### Pull Requests
- [ ] https://github.com/camunda/camunda-bpm-platform/pull/4321
- [ ] https://github.com/camunda/camunda-bpm-platform-maintenance/pull/1221

Dev2QA handover

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camunda / camunda-bpm-platform

During message correlation with `resultEnabled`, wrong entity is populated when "resultType": "Execution" #4310