feat(aws_docdb_cluster): add allow_major_version_upgrade argument

[gmeligio]

trafficstars

what

This PR adds the argument allow_major_version_upgrade that was released in https://github.com/hashicorp/terraform-provider-aws/releases/tag/v5.21.0

why

When upgrading the engine_version to a new major version, allow_major_version_upgrade needs to be enabled for AWS to apply the upgrade.

references

• https://github.com/hashicorp/terraform-provider-aws/releases/tag/v5.21.0
• https://awscli.amazonaws.com/v2/documentation/api/latest/reference/docdb/modify-db-cluster.html
• https://docs.aws.amazon.com/documentdb/latest/developerguide/docdb-mvu.html