[AWS::OpenSearchService::Domain] engine version upgrades should not be destructive by default

### Name of the resource

AWS::OpenSearchService::Domain

### Resource name

_No response_

### Description

I have several OpenSearch stacks provisioned using CloudFormation. I need to update the EngineVersion from 2.5 to 2.9, which should be seamless. However, if I do not specify the EnableVersionUpgrade UpdatePolicy, my entire domain and all data contained within will be deleted, per [1] and [2].

As an administrator, I believe that EngineVersionUpgrade = true behavior should be the **default** in this scenario, for the following reasons:
1. If I use the OpenSearch UI, CLI/API, or SDK [3] to upgrade versions, OpenSearch performs the upgrade seamlessly without requiring extra flags.
2. An extra flag to enable the behavior is confusing and dangerous. It could easily be missed by someone who did not refer back to the documentation before changing the version in the template.
3. If I DID want to delete all my data in a domain created by CloudFormation, I would simply delete the entire stack or the resource from the template.

I created support case [4] to address this issue, if you want to read through the details.

Thanks for considering this!

### Other Details

[1]
https://docs.aws.amazon.com/en_us/AWSCloudFormation/latest/UserGuide/aws-resource-opensearchservice-domain.html#cfn-opensearchservice-domain-engineversion
[2]
https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-attribute-updatepolicy.html#cfn-attributes-updatepolicy-upgradeopensearchdomain
[3]
https://docs.aws.amazon.com/opensearch-service/latest/developerguide/version-migration.html#starting-upgrades
[4]
Case ID 170024197001085

No source files, tests, or entry points are mentioned. Start by reviewing the AWS::OpenSearchService::Domain EngineVersion documentation, the UpdatePolicy upgrade behavior, and the linked OpenSearch migration guidance; done means engine upgrades no longer delete the domain or its data by default.

Written by the indexing model from the issue text.