Add `aws-smithy-observability` and `aws-smithy-observability-otel` crates (#4003)

## Motivation and Context
<!--- Why is this change required? What problem does it solve? -->
<!--- If it fixes an open issue, please link to the issue here -->
This PR is an updated version of
https://github.com/smithy-lang/smithy-rs/pull/3912 and
https://github.com/smithy-lang/smithy-rs/pull/3986

 moving back to the
`dyn Trait` based implementation since some issues came up in the review
of the Associated Types based implementation

## Description
<!--- Describe your changes in detail -->
Add two new crates
* `aws-smithy-observability` - contains traits for our observability
solution and a `global` module for managing the global telemetry
provider
* `aws-smithy-observability-otel` - contains an OpenTelemetry based
implementation of the traits

## Testing
<!--- Please describe in detail how you tested your changes -->
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to -->
<!--- see how your change affects other areas of the code, etc. -->
Various unit tests in both new crates.

## Checklist
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rather than leaving it unchecked -->
Note: leaving out a changelog entry for now since these crates won't
offer much value until we instrument our runtime crates in some
subsequent PRs

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Co-authored-by: Zelda Hessler <zhessler@amazon.com>