Update CHANGELOG.md for #46978

Author: changelogbot

CHANGELOG.md

@@ -25,6 +25,7 @@ FEATURES:
 ENHANCEMENTS:
 
 * resource/aws_datasync_task: Add `schedule.status` argument ([#46037](https://github.com/hashicorp/terraform-provider-aws/issues/46037))
+* resource/aws_docdbelastic_cluster: Add `shard_instance_count` argument ([#46938](https://github.com/hashicorp/terraform-provider-aws/issues/46938))
 * resource/aws_iam_user: Add resource identity support ([#46869](https://github.com/hashicorp/terraform-provider-aws/issues/46869))
 * resource/aws_s3_bucket: Add `bucket_namespace` argument in support of [account regional namespaces for general purpose buckets](https://docs.aws.amazon.com/AmazonS3/latest/userguide/gpbucketnamespaces.html#account-regional-gp-buckets) ([#46917](https://github.com/hashicorp/terraform-provider-aws/issues/46917))