stackdriver: fix Cargo features for GcpAuthorizer

[djc]

Changes

50 regressed the support for actually using the GcpAuthorizer: it used the dep:gcp_auth syntax for enabling the dependency by default, but the actual GcpAuthorizer code was guarded by a gcp_auth feature which didn't exist anymore. Bring back a named feature for this (now called gcp-authorizer to match yup-authorizer).

This time I will start a PR for my work repository based on my branch to make sure it actually works.

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 51.7%. Comparing base (a98f9be) to head (b89e0b5).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #51 +/- ## ======================================= - Coverage 51.9% 51.7% -0.3% ======================================= Files 37 37 Lines 4896 4918 +22 ======================================= Hits 2544 2544 - Misses 2352 2374 +22 ```

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[TommyCpp]

Merging this. @djc I think you are listed as owner of https://crates.io/crates/opentelemetry-stackdriver in crates.io. Do you want to publish a new version?

[djc]

Yeah, will do!

[djc]

Published 0.19.1 on crates.io.

[djc]

Interesting. I'd thought clippy would caught this

I think this is a weak spot in the toolchain, I think work is ongoing to fix it though.