Add and expose metrics in ObjectStore Trait

[mingmwang]

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The current ObjectStore Trait and implementations do not collect and expose any metrics. Add some metrics like read/write/delete ops counts, scan bytes, elapse times etc and expose them will be very useful in the production environment.

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[alamb]

One way to do this might be to implement a wrapper around an inner Arc<dyn ObjectStore> interface that had metrics.

Much like https://github.com/apache/arrow-rs/blob/master/object_store/src/limit.rs or https://github.com/apache/arrow-rs/blob/master/object_store/src/throttle.rs

BTW I plan to release a new object_store release (from arrow-rs) mid next week

Something like

struct TracingObjectStore {
  inner: Arc<dyn ObjectStore>
}

impl ObjectStore for TracingObjectStore { 
 fn get(&self) { 
   // add whatever tracing is needed
   self.inner.get()
  }
...
}