fix: add opensearch_acl to data.digitalocean_database_user schema

[andrewsomething]

This bug was introduced when opensearch_acl support was added to the database cluster resource (#1215). The resource and data source share the flattenUserSettings method. When the data source attempts to set the empty opensearch_acl to state, it errors as it is not part of the datasource schema.

terraform-provider-digitalocean/digitalocean/database/resource_database_user.go

Lines 348 to 357 in f27a112

	func flattenUserSettings(settings *godo.DatabaseUserSettings) []map[string]interface{} {
	result := make([]map[string]interface{}, 0, 1)
	if settings != nil {
	r := make(map[string]interface{})
	r["acl"] = flattenUserACLs(settings.ACL)
	r["opensearch_acl"] = flattenOpenSearchUserACLs(settings.OpenSearchACL)
	result = append(result, r)
	}
	return result
	}

The acceptance test did not catch this as the user needs to have a setting block in the API response as the method checks it settings is nil. A brand new Postgres user does not, but a doadmin user does, e.g.

{
  "user": {
    "name": "doadmin",
    "role": "primary",
    "password": "<redacted>",
    "settings": {
      "pg_allow_replication": true
    }
  }
}

Updated test now passes, but before the change would fail with:

panic: Invalid address to set: []string{"settings", "0", "opensearch_acl"}

Fixes: #1289

[loosla]

🙏 Thank you