[API] Add a new AddLink() operation to Span #8685

Job	Run time
Bazel asan config	11m 15s
Bazel noexcept	19m 15s
Bazel nortti	23m 28s
Bazel on MacOS	26m 14s
Bazel	22m 37s
Bazel with async export	19m 20s
Bazel tsan config	21m 11s
Bazel valgrind	22m 23s
Bazel with external abseil	26m 59s
Benchmark	17m 32s
CMake test (with abseil)	6m 33s
CMake clang 14 (maintainer mode, abiv2)	17m 21s
CMake clang 14 (maintainer mode, async)	22m 30s
CMake clang 14 (maintainer mode, sync)	17m 27s
CMake do not install test (with otlp-exporter)	20m 51s
CMake gcc 12 (maintainer mode, async)	10m 40s
CMake gcc 12 (maintainer mode, sync)	14m 41s
CMake install test (with abseil)	8m 16s
CMake test (with modern protobuf,grpc and abseil)	34m 10s
CMake msvc (maintainer mode)	9m 55s
CMake test (with opentracing-shim)	7m 52s
CMake test (build shared libraries with otlp-exporter and static gRPC)	24m 51s
CMake test (with otlp-exporter)	21m 59s
CMake test (without otlp-exporter)	7m 46s
CMake C++14 test(GCC)	6m 48s
CMake C++17 test(GCC)	6m 51s
CMake C++20 test(Clang with libc++)	13m 52s
CMake C++20 test(GCC)	12m 48s
CMake test (without otlp-exporter and with async export)	6m 57s
Code coverage	13m 12s
Copyright	9s
Format	28s
DocFX check	1m 19s
markdown-lint	14s
misspell	7s
Plugin -> CMake	2m 37s
CMake -> exporter proto	17m 36s
Bazel Windows	33m 35s
Plugin -> CMake Windows	9m 30s
CMake (With async export) -> exporter proto	18m 41s
CMake -> exporter proto (Build as DLL)	18m 12s
	9h 58m 2s

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