fix(logging): Use instance/attributes/cluster-location for location on GKE

[gkevinzheng]

Use instance/attributes/cluster-location for location on GKE to set the value of location to the cluster location as opposed to just the zone, to bring it in line with what other logging libraries do: see https://github.com/googleapis/google-cloud-cpp/blob/4ba2cc4d1d0cfdd70dec6d1affb26423d0e9dac1/google/cloud/opentelemetry/internal/resource_detector_impl.cc#L103C51-L103C67 and https://github.com/googleapis/google-cloud-cpp/blob/850564f330ac6e918d6d40ac1ab17a200282a196/google/cloud/opentelemetry/internal/monitored_resource.cc#L88 for C++, and for what is tagged under location in other GKE logging statements.

See also https://cloud.google.com/kubernetes-engine/docs/concepts/workload-identity#instance_metadata

Fixes #9083 #9070

[arekkusu]

Thanks. Once this is merged, I imagine it will be mentioned in the next release change log.

For users writing k8s_container log using this library this fix might have some impact such as existing log filters (for example used within alert policy...) no longer working as before. This is if they actually rely (filter on) the "location" label. Unfortunately there is simply no way around this.