[Logs SDK] Log Appender for spdlog

[chusitoo]

Implemented as described in open-telemetry/opentelemetry-cpp#2046:

• Sink implemented in spdlog::sinks namespace for commonality with existing sinks.
• Minimal examples provided to demonstrate the setup required.
• Basic unit testing.
• Tried using the same flags as those used in otel-cpp for configuring cmake project.
• Add clang format file to help keep the style in line with otel-cpp repo.

[ndl]

This should either use string_view(msg.payload.data(), msg.payload.size()) or string_view(msg.payload.c_str()) to avoid out-of-bounds access?

[chusitoo]

Makes sense, thanks! Good catch.

[ndl]

Probably also makes sense to export the target itself so that it's easier to use this library in another cmake-based project, smth like

  install(
    EXPORT "${PROJECT_NAME}-target"
    FILE "${PROJECT_NAME}-target.cmake"
    NAMESPACE "${PROJECT_NAME}::"
    DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/${PROJECT_NAME})

?

Ideally also a config (see e.g. https://cmake.org/cmake/help/latest/guide/importing-exporting/index.html#creating-a-package-configuration-file) for easier discoverability / reuse?

[chusitoo]

That's reasonable, I'll have a look. I was seeing it as a Makefile-based build only.

[marcalff]

Thanks for the contribution.