ci: apply gRPC SSL workaround to reduce flakes in demo builds

[scotthart]

No description provided.

[gemini-code-assist]

Code Review

This pull request updates the gRPC version from v1.71.2 to v1.84.0 across several demo Dockerfiles and the packaging documentation, while switching the SSL provider configuration from package to module and adding manual downloads for grpc-proto and BoringSSL. The feedback advises against propagating these BoringSSL module workarounds to the public packaging documentation (doc/packaging.md), as standard Linux distribution packaging guidelines require linking against the system-provided OpenSSL package to ensure automatic security updates.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.39%. Comparing base (c0e675a) to head (492b258).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16552      +/-   ##
==========================================
+ Coverage   92.37%   92.39%   +0.01%     
==========================================
  Files        2266     2266              
  Lines      219493   219493              
==========================================
+ Hits       202765   202797      +32     
+ Misses      16728    16696      -32     

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