### Elasticsearch Version

main

### Installed Plugins

_No response_

### Java Version

_bundled_

### OS Version

MacOS

### Problem Description

When there are 2 or more concurrent `_update` requests issued, one of them may fail with `ResourceAlreadyExistsException` exception which is misleading.


### Steps to Reproduce

1. Spawn a number of `_update` requests at the same time
2. Look at the results of these requests
3. Observe `ResourceAlreadyExistsException` being thrown in the case of conflict

### Logs (if relevant)

_No response_
x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/transform/TransformMessages.java
public static final String FAILED_TO_CREATE_DESTINATION_INDEX = "Could not create destination index [{0}] for transform [{1}]";
    public static final String FAILED_TO_SET_UP_DESTINATION_ALIASES =
        "Could not set up aliases for destination index [{0}] for transform [{1}]";
    public static final String FAILED_TO_RELOAD_TRANSFORM_CONFIGURATION = "Failed to reload transform configuration for transform [{0}]";
    public static final String FAILED_TO_LOAD_TRANSFORM_CONFIGURATION = "Failed to load transform configuration for transform [{0}]";
    public static final String FAILED_TO_PARSE_TRANSFORM_CONFIGURATION = "Failed to parse transform configuration for transform [{0}]";
    public static final String FAILED_TO_PARSE_TRANSFORM_STATISTICS_CONFIGURATION =
        "Failed to parse transform statistics for transform [{0}]";
    public static final String FAILED_TO_LOAD_TRANSFORM_CHECKPOINT = "Failed to load transform checkpoint for transform [{0}]";
    public static final String FAILED_TO_LOAD_TRANSFORM_STATE = "Failed to load transform state for transform [{0}]";
    public static final String TRANSFORM_CONFIGURATION_BAD_FUNCTION_COUNT = "Transform configuration must specify exactly 1 function";
    public static final String TRANSFORM_CONFIGURATION_PIVOT_NO_GROUP_BY = "Pivot transform configuration must specify at least 1 group_by";
    public static final String TRANSFORM_CONFIGURATION_PIVOT_NO_AGGREGATION =
        "Pivot transform configuration must specify at least 1 aggregation";
    public static final String TRANSFORM_FAILED_TO_CREATE_COMPOSITE_AGGREGATION =
        "Failed to create composite aggregation from {0} function";
    public static final String TRANSFORM_CONFIGURATION_INVALID = "Transform configuration [{0}] has invalid elements: [{1}]";
    public static final String TRANSFORM_CONFIGURATION_DEPRECATED = "Transform configuration is at version [{0}]. Use [{1}] or ["
        + TransformField.REST_BASE_PATH_TRANSFORMS
        + "_upgrade] to update.";
    public static final String UNABLE_TO_GATHER_FIELD_MAPPINGS = "Failed to gather field mappings for index [{0}]";
    public static final String TRANSFORM_UPDATE_CANNOT_CHANGE_SYNC_METHOD =
        "Cannot change the current sync configuration of transform [{0}] from [{1}] to [{2}]";
    public static final String LOG_TRANSFORM_CONFIGURATION_BAD_QUERY = "Failed to parse query for transform";
    public static final String LOG_TRANSFORM_CONFIGURATION_BAD_SCRIPT = "Failed to parse script for transform";
    public static final String LOG_TRANSFORM_CONFIGURATION_BAD_GROUP_BY = "Failed to parse group_by for pivot transform";
    public static final String LOG_TRANSFORM_CONFIGURATION_BAD_AGGREGATION = "Failed to parse aggregation for pivot transform";
    public static final String LOG_TRANSFORM_PIVOT_REDUCE_PAGE_SIZE =
        "Insufficient memory for search, reducing number of buckets per search from [{0}] to [{1}]";
    public static final String LOG_TRANSFORM_PIVOT_LOW_PAGE_SIZE_FAILURE =