Tag shows manadatory for host availability event rule

[avneeshsardana]

Hi team,

Instana Provider doesn't allow creation of host availability custom event whose scope applies on all entities rather than scope host by tag.

Provider shows tag field as required https://registry.terraform.io/providers/instana/instana/latest/docs/resources/custom_event_specification#host-availability-rule.

Please keep the tag field as optional or suggest any way to create host availability custom event whose scope applied to all entities in organisation.