Fix EcsRunTaskOperator deferred-logs region and template field init

[fat-catTW]

Move EcsRunTaskOperator template-field decisions out of __init__ so templated values are rendered before they affect ECS log handling.

This removes the operator from the validate_operators_init exemption list.

Besides moving the template-field logic out of __init__ (so templated awslogs_region/region_name values are rendered before they take effect), this also fixes a real bug in the deferrable path: execute_complete built its AwsLogsHook with region_name=self.region_name, so when awslogs_region was explicitly set to a different region than the task's region, the final log fetch after deferral queried CloudWatch in the wrong region and found no log stream. The new resolve_awslogs_region() helper is now the single place the log region is resolved (explicit awslogs_region, falling back to region_name), and both execute_complete and the task log fetcher use it. Note this covers only the post-deferral fetch — log forwarding during deferral still uses the task region inside TaskDoneTrigger; that remaining half is tracked in #70465.

related: #70296

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[shahar1]

Nice! You might haven't notice, but you probably fixed another bug as well :)

[fat-catTW]

Thanks!
I missed that at first too, but yes, this also makes execute_complete() honor awslogs_region in deferrable mode instead of always using region_name when fetching the final CloudWatch log event.