Add exemplar reservoir to async metric storage (#2319) #8500

Job	Run time
Bazel asan config	13m 35s
Bazel noexcept	26m 14s
Bazel nortti	19m 10s
Bazel on MacOS	25m 58s
Bazel	18m 42s
Bazel with async export	19m 7s
Bazel tsan config	21m 6s
Bazel valgrind	22m 30s
Bazel with external abseil	19m 59s
Benchmark	16m 53s
CMake test (with abseil)	6m 28s
CMake clang 14 (maintainer mode, async)	17m 18s
CMake clang 14 (maintainer mode, sync)	16m 57s
CMake do not install test (with otlp-exporter)	28m 14s
CMake gcc 4.8 (with otlp exporter)	19m 31s
CMake gcc 4.8 (without otlp exporter)	7m 59s
CMake gcc 12 (maintainer mode, async)	11m 44s
CMake gcc 12 (maintainer mode, C++11, async)	10m 17s
CMake gcc 12 (maintainer mode, sync)	11m 18s
CMake install test (with abseil)	6m 2s
CMake test (with modern protobuf,grpc and abseil)	33m 53s
CMake msvc (maintainer mode)	14m 6s
CMake test (with opentracing-shim)	6m 35s
CMake test (build shared libraries with otlp-exporter and static gRPC)	21m 45s
CMake test (with otlp-exporter)	21m 12s
CMake test (without otlp-exporter)	8m 43s
CMake C++20 test(Clang with libc++)	11m 50s
CMake C++20 test(GCC)	12m 23s
CMake test (without otlp-exporter and with async export)	6m 37s
Code coverage	16m 33s
Copyright	10s
DocFX check	1m 18s
Format	18s
markdown-lint	10s
misspell	5s
Plugin -> CMake	1m 37s
CMake -> exporter proto	20m 39s
Bazel Windows	38m 44s
Plugin -> CMake Windows	13m 3s
CMake (With async export) -> exporter proto	23m 33s
CMake -> exporter proto (Build as DLL)	17m 52s
	10h 10m 8s

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