Update C++ documentations

[dmehala]

What does this PR do? What is the motivation?

Merge instructions

• [ ] Please merge after reviewing

Additional notes

Draft to generate previews 👀

[github-actions[bot]]

Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/dmehala/cpp-updates/getting_started/tagging/unified_service_tagging
• https://docs-staging.datadoghq.com/dmehala/cpp-updates/tracing/guide/setting_up_APM_with_cpp
• https://docs-staging.datadoghq.com/dmehala/cpp-updates/tracing/trace_collection/automatic_instrumentation/dd_libraries/cpp
• https://docs-staging.datadoghq.com/dmehala/cpp-updates/tracing/trace_collection/compatibility/cpp
• https://docs-staging.datadoghq.com/dmehala/cpp-updates/tracing/trace_collection/custom_instrumentation/cpp/dd-api
• https://docs-staging.datadoghq.com/dmehala/cpp-updates/tracing/trace_collection/library_config/cpp
• https://docs-staging.datadoghq.com/dmehala/cpp-updates/tracing/trace_collection/runtime_config/
• https://docs-staging.datadoghq.com/dmehala/cpp-updates/tracing/trace_collection/trace_context_propagation/cpp
• https://docs-staging.datadoghq.com/dmehala/cpp-updates/tracing/trace_pipeline/ingestion_mechanisms

[dmehala]

TODO:

• ~~https://docs.datadoghq.com/tracing/guide/setting_up_apm_with_cpp/~~
• ~~https://docs.datadoghq.com/getting_started/tagging/unified_service_tagging/?tab=kubernetes~~
• French?

[hestonhoffman]

Added an editorial card for this one

[dmehala]

There's one comment left for compiler vs toolchain. You make the call @brett0000FF, unless there's anything else, that PR is ready to merge. Thank you for reviewing, I appreciate.