[API] Add a new AddLink() operation to Span #8688

Job	Run time
CMake clang 14 (maintainer mode, sync)	16m 46s
CMake test (without otlp-exporter)	6m 43s
CMake gcc 12 (maintainer mode, async)	11m 0s
CMake clang 14 (maintainer mode, async)	17m 15s
CMake test (with abseil)	6m 31s
CMake clang 14 (maintainer mode, abiv2)	17m 4s
CMake gcc 12 (maintainer mode, sync)	12m 35s
CMake msvc (maintainer mode)	10m 58s
CMake C++14 test(GCC)	5m 52s
CMake C++17 test(GCC)	6m 57s
CMake C++20 test(GCC)	14m 51s
CMake test (without otlp-exporter and with async export)	6m 37s
Bazel noexcept	18m 27s
Bazel nortti	22m 14s
Bazel	20m 39s
Bazel with async export	19m 27s
Bazel valgrind	26m 16s
Bazel with external abseil	21m 34s
CMake do not install test (with otlp-exporter)	20m 32s
CMake install test (with abseil)	7m 32s
CMake test (with modern protobuf,grpc and abseil)	33m 13s
CMake test (with opentracing-shim)	6m 33s
CMake test (build shared libraries with otlp-exporter and static gRPC)	20m 25s
CMake test (with otlp-exporter)	22m 29s
CMake C++20 test(Clang with libc++)	11m 8s
Plugin -> CMake	1m 42s
Bazel asan config	11m 54s
Bazel on MacOS	14m 11s
Bazel tsan config	19m 57s
Benchmark	12m 10s
Code coverage	14m 6s
Copyright	6s
DocFX check	52s
Format	21s
markdown-lint	9s
misspell	9s
CMake -> exporter proto	21m 53s
Bazel Windows	41m 20s
Plugin -> CMake Windows	12m 3s
CMake (With async export) -> exporter proto	17m 55s
CMake -> exporter proto (Build as DLL)	16m 50s
	9h 29m 16s

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