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

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

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

Additional details and impacted files

@@           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!