### Description

Currently, when we execute retention policy, we also refresh the destination index by setting:
```
setRefresh(true)
```
on the DBQ request.
This can cause permission errors which are surprising to the user as the permissions are not required when the transform starts:
```
task encountered irrecoverable failure: org.elasticsearch.ElasticsearchSecurityException: action [indices:admin/refresh] is unauthorized for user [found-internal-kibana4-server] with roles [kibana_system,found-internal-kibana4-server] on indices [logs-cloud_security_posture.findings_latest-default], this action is granted by the index privileges [maintenance,manage,all]
```

We still want the user to have the permissions to delete the documents. But we should execute `refresh` as the system user.
x-pack/plugin/transform/src/test/java/org/elasticsearch/xpack/transform/transforms/RetentionPolicyConfigToDeleteByQueryTests.java
assertNull(
            RetentionPolicyToDeleteByQueryRequestConverter.buildDeleteByQueryRequest(
                randomRetentionPolicyConfig(),
                SettingsConfigTests.randomSettingsConfig(),
                DestConfigTests.randomDestConfig(),
                null
            )
        );
        
        assertNull(
            RetentionPolicyToDeleteByQueryRequestConverter.buildDeleteByQueryRequest(
                randomRetentionPolicyConfig(),
                SettingsConfigTests.randomSettingsConfig(),
                DestConfigTests.randomDestConfig(),
                TransformCheckpoint.EMPTY
            )
        );
    }
    public void testTimeBasedRetentionPolicyConfig() {
        SettingsConfig settingsConfig = SettingsConfigTests.randomSettingsConfig();
        DestConfig destConfig = DestConfigTests.randomDestConfig();
        RetentionPolicyConfig retentionPolicyConfig = new TimeRetentionPolicyConfig(
            randomAlphaOfLengthBetween(3, 5),
            new TimeValue(60_000L)
        );
        TransformCheckpoint checkpoint = new TransformCheckpoint(
            randomAlphaOfLengthBetween(3, 5),
            10_000_000L,
            1,