[EXAMPLES] Improve readme of Metrics example #9092

Job	Run time
CMake clang 15 (maintainer mode, abiv2)	13m 57s
CMake clang 15 (maintainer mode, async)	13m 57s
CMake clang 15 (maintainer mode, sync)	14m 11s
CMake gcc 13 (maintainer mode, async)	6m 48s
CMake gcc 13 (maintainer mode, sync)	6m 42s
CMake msvc (maintainer mode)	8m 7s
CMake test (without otlp-exporter)	5m 6s
CMake test (with abseil)	4m 25s
CMake msvc (maintainer mode) with C++20	8m 35s
CMake C++14 test(GCC)	4m 13s
CMake test (with opentracing-shim)	4m 22s
CMake test (without otlp-exporter and with async export)	5m 10s
CMake test (with otlp-exporter)	13m 51s
CMake C++20 test(Clang with libc++)	9m 18s
CMake C++20 test(GCC)	9m 7s
CMake C++17 test(GCC)	4m 29s
CMake C++23 test(GCC)	9m 0s
CMake C++23 test(Clang with libc++)	9m 35s
Bazel noexcept	12m 12s
Bazel	13m 3s
Bazel with async export	12m 54s
Bazel valgrind	14m 8s
Bazel with external abseil	12m 54s
CMake do not install test (with otlp-exporter)	13m 39s
CMake install test (with abseil)	4m 22s
CMake test (with modern protobuf,grpc and abseil)	18m 33s
CMake test (build shared libraries with otlp-exporter and static gRPC)	14m 29s
Plugin -> CMake	1m 17s
Bazel asan config	15m 6s
Bazel nortti	12m 46s
Bazel on MacOS	36m 38s
Bazel tsan config	13m 12s
Benchmark	8m 15s
Code coverage	11m 45s
Copyright	7s
DocFX check	41s
Format	12s
markdown-lint	6s
misspell	3s
CMake -> exporter proto	12m 17s
Bazel Windows	21m 48s
Plugin -> CMake Windows	6m 30s
CMake (With async export) -> exporter proto	12m 3s
CMake -> exporter proto (Build as DLL)	26m 47s
	7h 26m 40s

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