AWS::Elasticsearch::Domain - Auto-Tune

## Scope of request
ES got a new feature [Auto-tune]( https://aws.amazon.com/about-aws/whats-new/2021/03/amazon-elasticsearch-service-announces-auto-tune-feature-improved-performance-application-availability/). This feature with all its options are not supported by AWS Cloudformation.

Options missing:
- Auto-Tune: Enabled State
- Maintenance Windows: State
- ScheduledAutoTuneDetails

[API Specification - CreateElasticSearchDomain - AutoTuneOptions](https://awsapichanges.info/archive/changes/66ea51-es.html)
```json
{'AutoTuneOptions': {'DesiredState': 'ENABLED | DISABLED',
'MaintenanceSchedules': [{'CronExpressionForRecurrence': 'string',
'Duration': {'Unit': 'HOURS',
'Value': 'long'},
'StartAt': 'timestamp'}]}}
```

## Expected behavior

Configure the options for ES Auto-tune via Cloudformation - see Screenshot of console:


## Suggest specific test cases

none

## Helpful Links to speed up research and evaluation

- New Feature Announcement: https://aws.amazon.com/about-aws/whats-new/2021/03/amazon-elasticsearch-service-announces-auto-tune-feature-improved-performance-application-availability/
- https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-elasticsearch-domain.html
- https://awsapichanges.info/archive/changes/66ea51-es.html

## Category (required)
- Analytics (Athena, EMR, Glue,...)

Start at the AWS::Elasticsearch::Domain resource and compare the CloudFormation resource documentation with the linked AutoTuneOptions API specification. Trace how domain properties are represented and tested in this repository, then add support for DesiredState and MaintenanceSchedules so Auto-Tune can be configured through CloudFormation. The issue provides no specific files or test cases, so identify the relevant implementation and test entry points first.

Written by the indexing model from the issue text.