GCP WIF impersonation (LibSFC)

[sfc-gh-ddas]

SNOW-2236576 | SNOW-2236579: Transitive service account impersonation

Added support for service account impersonation using comma separated delegation chain for GCP.

The change was based off logic in JDBC equivalent and tested using unit tests with a mock HTTP client.

Depends on #950

[codecov]

Codecov Report

❌ Patch coverage is 11.30435% with 102 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.85%. Comparing base (b29a564) to head (1beee8f).
⚠️ Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
cpp/GcpAttestation.cpp	12.03%	95 Missing ⚠️
cpp/http/HttpClient.cpp	0.00%	3 Missing ⚠️
cpp/AwsAttestation.cpp	0.00%	2 Missing ⚠️
cpp/AzureAttestation.cpp	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #949      +/-   ##
==========================================
- Coverage   79.51%   78.85%   -0.66%     
==========================================
  Files         127      127              
  Lines       10870    11016     +146     
==========================================
+ Hits         8643     8687      +44     
- Misses       2227     2329     +102     

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