Investigate automatic detection of CA roots from environment variables (e.g. CURL_CA_BUNDLE)

[jinseopkim0]

Problem
Currently, to make the quickstart examples work in the Windows Bazel CI environment (which uses a hermetic build with custom OpenSSL roots), we explicitly modify the C++ code to read the CURL_CA_BUNDLE environment variable and set the CARootsFilePathOption.

See PR #15818 for the current implementation

Goal
We should explore ways to avoid modifying the example code (quickstart.cc) for this CI-specific configuration.

Potential Solutions

• Update the client library to automatically check CURL_CA_BUNDLE or standard OpenSSL environment variables when initializing the default Options.
• Adjust the Bazel build configuration to transparently point to the correct roots without code changes.

This issue tracks the investigation and implementation of a solution that keeps the quickstart code clean and environment-agnostic.