Update Rust crate tracing-opentelemetry to 0.21.0

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
tracing-opentelemetry	workspace.dependencies	minor	0.20.0 -> 0.21.0

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Release Notes

tokio-rs/tracing-opentelemetry (tracing-opentelemetry)

v0.21.0

Compare Source

Added

• Ability to produce measurement with attributes (#​43)

Breaking Changes

• MetricsLayer is now generic over the its Subscriber impl to support
  per-layer filtering (#​43)

Fixed

• Trace IDs not matching when propagating invalid contexts (#​55)

Thanks to @​ymgyt and @​hdost for contributing to this release!

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