impl(gax-internal): fallback on URL for server address

[coryan]

Fixes #5144

[codecov]

Codecov Report

❌ Patch coverage is 96.92308% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.90%. Comparing base (b8f8f74) to head (11c01ac).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...ernal/src/observability/client_signals/recorder.rs	96.82%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5155      +/-   ##
==========================================
- Coverage   97.90%   97.90%   -0.01%     
==========================================
  Files         213      213              
  Lines       42664    42720      +56     
==========================================
+ Hits        41772    41825      +53     
- Misses        892      895       +3     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.