Observability DA is missing the ability to set metrics routing primary region which fails deployment in fresh account

[ocofaigh]

When running the latest version of the Observability DA in a new account, the following error was seen:

Error: CreateTargetWithContext failed Your request has failed because metadata_primary_region in settings is empty. Please set the metadata_region_primary and then try again.

with module.observability_instance.module.metric_routing.ibm_metrics_router_target.metrics_router_targets["rag-new-cloud-monitoring-target"]

The metadata_region_primary can be set using the metrics_router_settings input variable in the terraform-ibm-observability-instances however no such input has been exposed in the Observability DA.

Since this seems to be required to create a metrics routing target, we should expose the ability to set this in the DA. If it makes sense, perhaps add default values using best practice settings (maybe consult with metrics routing team on best defaults to use).

NOTE: This error was not seen in the GoldenEye dev account because it already has a primary region set in its settings from PR pipeline tests. It was only seen on a new fresh account so suggest to do all testing in a fresh enterprise sub account.

We have the same gap for the Activity tracker settings too, so suggest to also plug that too. The module has an input called global_event_routing_settings for those settings.