add http server example with `io_uring` #2174

Job	Run time
Linux GCC 9 Debug (C++17)	3m 16s
Linux GCC 9 Optimised (C++17)	4m 47s
Linux GCC 9 Debug (C++20)	3m 15s
Linux GCC 9 Optimised (C++20)	4m 39s
Linux GCC 10 Debug (C++17)	3m 18s
Linux GCC 10 Optimised (C++17)	3m 11s
Linux GCC 10 Debug (C++20)	4m 29s
Linux GCC 10 Optimised (C++20)	4m 3s
Linux GCC 10 Debug (C++20) w/coroutines	4m 40s
Linux GCC 10 Optimised (C++20) w/coroutines	5m 43s
Linux Clang 10 Debug (C++17)	3m 9s
Linux Clang 10 Optimised (C++17)	3m 56s
Linux Clang 10 Debug (C++20)	4m 7s
Linux Clang 10 Optimised (C++20)	4m 17s
Linux Clang 11 Debug (C++17)	3m 24s
Linux Clang 11 Optimised (C++17)	5m 29s
Linux Clang 11 Debug (C++20)	4m 55s
Linux Clang 11 Optimised (C++20)	4m 27s
Linux Clang 12 Debug (C++17)	3m 37s
Linux Clang 12 Optimised (C++17)	4m 13s
Linux Clang 12 Debug (C++20)	4m 9s
Linux Clang 12 Optimised (C++20)	5m 8s
macOS GCC Debug (C++17)	3m 5s
macOS GCC Optimised (C++17)	4m 1s
macOS GCC Debug (C++20)	2m 37s
macOS GCC Optimised (C++20)	4m 55s
macOS Clang Debug (C++17)	1m 35s
macOS Clang Optimised (C++17)	4m 4s
macOS Clang Debug (C++20)	2m 11s
macOS Clang Optimised (C++20)	3m 31s
Windows MSVC 2019 Debug (C++17)	1m 29s
Windows MSVC 2019 Optimised (C++17)	1m 26s
Windows MSVC 2019 Debug (C++20)	6m 15s
Windows MSVC 2019 Optimised (C++20)	6m 58s
	2h 14m 19s

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