Add support for compatibility_mode in elasticstack_kibana_import_saved_objects

[Karim-Othman]

Description:

When copying integration dashboards (e.g., Kubernetes/Fleet-managed dashboards) from one Kibana space to another using the elasticstack_kibana_import_saved_objects resource, the hyperlinks between overview dashboards and sub-dashboards break.

This seems to be related to how the import is handled. If the same dashboards are imported manually with the Kibana Saved Objects API and the ?compatibilityMode=true parameter, the links remain intact and navigation works as expected.

Example of working API import:

curl -u elastic-user -X POST \
  'https://Kibana-Host:port/s/<NewSpaceName>/api/saved_objects/_import?compatibilityMode=true' \
  -H "kbn-xsrf: true" \
  --form file=@export.ndjson

Problem:
The Terraform provider currently does not expose a compatibility_mode argument for elasticstack_kibana_import_saved_objects. This prevents Terraform users from achieving the same behavior as the API and results in broken dashboard navigation when moving dashboards across spaces.

Proposed Feature:

Add support for a compatibility_mode argument in elasticstack_kibana_import_saved_objects.

Impact / Use Case:

In multi-space environments, dashboards often need to be copied between spaces.

Without compatibility_mode, cross-dashboard links break, requiring manual intervention.

Supporting this flag will bring the Terraform provider in line with the Kibana Saved Objects Import API and improve automation workflows.
Similar to overwrite, it could default to false and be explicitly enabled by the user when required.

References:

Kibana Saved Objects Import API docs: https://www.elastic.co/docs/api/doc/kibana/v8/operation/operation-importsavedobjectsdefault

Provider schema where the option is currently missing:

terraform-provider-elasticstack/internal/kibana/import_saved_objects/schema.go

Line 142 in 45b2447

// CompatibilityMode types.Bool `tfsdk:"compatibility_mode"`