Add tracing for resolved endpoint

[rcoh]

Motivation and Context

It's sometimes useful to see the resolved endpoint URI, signing scope and signing region for debugging.

Description

Add tracing debug event during endpoint resolution

Testing

• manually verified that a sensible log line is printed:

resolved endpoint endpoint=AwsEndpoint { 
  endpoint: Endpoint { uri: https://ecr-fips.us-east-1.amazonaws.com/, immutable: false }, 
  credential_scope: CredentialScope { region: Some(SigningRegion("us-east-1")), service: None } } base_region=Region("fips-dkr-us-east-1")

Checklist

• I have updated CHANGELOG.md
• I have updated aws/SDK_CHANGELOG.md if applicable

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

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A new generated diff is ready to view: __generated-main...__generated-log-endpoint

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[crisidev]

LGTM

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A new generated diff is ready to view: __generated-main...__generated-log-endpoint