Allow clients to define custom callbacks to handle telemetry

[aws-hans-pistor]

Description of change

Different users of mountpoint will care about different metrics returned for each requests, so allow them to define their own custom handlers for the on_telemetry callback in addition to the default metrics that mountpoint emits.

This allows users to do things like:

• emit extended request ids ("x-amz-id-2")
• When some criteria is met, log out additional information

Relevant issues: #1079

Does this change impact existing behavior?

No there should be no breaking changes, the only visible change is that there's a new field to the S3ClientConfig which defines the custom telemetry handler

Does this change need a changelog entry in any of the crates?

Just a note in mountpoint-s3-client letting users know this feature now exists

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and I agree to the terms of the Developer Certificate of Origin (DCO).

[aws-hans-pistor]

I've rebased back onto upstream's mainline

[vladem]

LGTM, one minor suggestion. Launched the tests, ready to approve after that.

[aws-hans-pistor]

The failing test seems unrelated

mountpoint-s3/mountpoint-s3/src/upload/incremental.rs

Line 234 in 33c20c8

let checksum_algorithm = self.checksum_algorithm.get_mut().await?.unwrap().clone();

 ---- upload::incremental::tests::test_append_failure_on_object_replaced stdout ----
thread 'upload::incremental::tests::test_append_failure_on_object_replaced' panicked at mountpoint-s3/src/upload/incremental.rs:234:75: