Support Auto AZ Selection Mechanism for ECS

[cboelle]

Description of the enhancement

The new API for ECS supports a random selection based on flavor availability and capacity across all AZ’s. Would be create to have TF support and hint in the documentation how to use.

availability_zone = empty 
batch_create_in_multi_az = true

https://docs.otc.t-systems.com/elastic-cloud-server/api-ref/apis_recommended/lifecycle_management/creating_an_ecs.html

[anton-sidelnikov]

Hi @cboelle, we can't include such attribute into terraform, randomization always gives a huge pain to handle within state, and availability_zone is forceNew parameter we also cant set it as empty. Need to think deeper how to properly handle this.