Support a system-wide OpenSSL installation

[jviotti]

Signed-off-by: Juan Cruz Viotti jv@jviotti.com

[cubic-dev-ai]

No issues found across 6 files

[augmentcode]

🤖 Augment PR Summary

Summary: Adds an option to build Hydra against a system OpenSSL installation instead of the vendored mbedTLS.
Changes:

• Introduces SOURCEMETA_HYDRA_USE_SYSTEM_OPENSSL and wires it through CI and the Makefile.
• When enabled, finds OpenSSL at configure-time and configures the vendored curl build to use it.
• Updates the installed package config to find_dependency(OpenSSL) (or mbedTLS otherwise) for consumers.
• Propagates the option into the packaging/find_package CMake test configuration.

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[augmentcode]

Review completed. 2 suggestions posted.

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