[EXPORTER] Support URL-encoded values for `OTEL_EXPORTER_OTLP_HEADERS` #9295

Job	Run time
CMake clang 15 (maintainer mode, abiv2)	13m 57s
CMake clang 15 (maintainer mode, async)	13m 52s
CMake clang 15 (maintainer mode, sync)	14m 3s
CMake gcc 13 (maintainer mode, async)	6m 51s
CMake gcc 13 (maintainer mode, sync)	6m 43s
CMake test (without otlp-exporter)	4m 55s
CMake test (with abseil)	4m 20s
CMake msvc (maintainer mode)	7m 16s
CMake msvc (maintainer mode) with C++20	8m 34s
CMake test (with opentracing-shim)	4m 20s
CMake C++14 test(GCC)	4m 2s
CMake C++17 test(GCC)	4m 52s
CMake C++20 test(Clang with libc++)	9m 17s
CMake C++20 test(GCC)	8m 39s
CMake C++23 test(GCC)	8m 40s
CMake test (without otlp-exporter and with async export)	5m 3s
Bazel asan config	14m 38s
Bazel noexcept	12m 1s
Bazel nortti	12m 22s
Bazel	12m 19s
Bazel tsan config	13m 15s
Bazel valgrind	13m 42s
Bazel with external abseil	11m 47s
Bazel with async export	12m 13s
CMake do not install test (with otlp-exporter)	13m 47s
CMake install test (with abseil)	4m 12s
CMake test (with modern protobuf,grpc and abseil)	18m 5s
CMake test (build shared libraries with otlp-exporter and static gRPC)	13m 16s
CMake test (with otlp-exporter)	14m 17s
CMake C++23 test(Clang with libc++)	9m 39s
Plugin -> CMake	52s
Bazel on MacOS	15m 20s
Benchmark	7m 55s
Code coverage	11m 41s
Copyright	5s
DocFX check	57s
Format	15s
markdown-lint	5s
misspell	3s
CMake -> exporter proto	12m 32s
Bazel Windows	20m 37s
Plugin -> CMake Windows	6m 14s
CMake (With async export) -> exporter proto	12m 17s
CMake -> exporter proto (Build as DLL)	22m 24s
	6h 52m 14s

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