Create helpers to initialize and export gRPC metrics

[coryan]

Starting with gRPC-v1.62.x there are cool metrics published via OTel:

https://github.com/grpc/grpc/blob/6d7a55890e076a3a8abc8185b6bf0153fcf9d179/include/grpcpp/ext/otel_plugin.h#L45-L58

We would like a simple function to initialize a metrics provider such that metrics related to the Storage library get exported to Cloud Monitoring. Presumably other libraries can use something similar.

Though we would probably need >= v1.63.0 to provide good filtering:

https://github.com/grpc/grpc/blob/bc470e47ad64ae94ba8baff01e75a7606ed1cd00/include/grpcpp/ext/otel_plugin.h#L125-L127

One issue is to figure out the right filtering function that works for universe domains, VPC-SC, and PSC.

• [x] #14112
• [x] Initialize the endpoint for the exporter
• [x] Initialize gRPC exporter only once per "endpoint"
• [x] Update monitored resource type to storage.googleapis.com/Client
• [x] Change metric names to use / as a separator instead of the . separators produced by gRPC
• [ ] Use resource detector to initialize the resource attributes in the exporter
• [ ] Configure the exporter to use CreateServiceTimeSeries()
• [ ] Configure the exporter to use the right prefix for the metric name

[coryan]

We need a function that will accept:

Target	Authority
storage.${universe_domain}	storage.${universe_domain}
private.googleapis.com	storage.googleapis.com
restricted.googleapis.com	storage.googleapis.com
storage-${foo}.p.googleapis.com	storage.googleapis.com

It should reject everything else.