stackdriver: prepare for release

[djc]

Changes

• Update to latest gcp_auth (0.11.0)
• Switches the default authenticator to gcp_auth (which I've always used, and which I maintain)
• Update changelog

Merge requirement checklist

• [x] CONTRIBUTING guidelines followed
• [x] Unit tests added/updated (if applicable)
• [x] Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• [x] Changes in public API reviewed (if applicable)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 51.0%. Comparing base (feb97a1) to head (1f6eb7e).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #50 +/- ## ======================================= + Coverage 50.5% 51.0% +0.4% ======================================= Files 34 34 Lines 4397 4358 -39 ======================================= Hits 2223 2223 + Misses 2174 2135 -39 ```

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[cijothomas]

https://crates.io/crates/opentelemetry-stackdriver/0.19.0 released

[djc]

Thanks!