add http server example with `io_uring` #2175

Job	Run time
Linux GCC 9 Debug (C++17)	4m 12s
Linux GCC 9 Optimised (C++17)	3m 59s
Linux GCC 9 Debug (C++20)	3m 48s
Linux GCC 9 Optimised (C++20)	5m 3s
Linux GCC 10 Debug (C++17)	3m 0s
Linux GCC 10 Optimised (C++17)	3m 31s
Linux GCC 10 Debug (C++20)	3m 44s
Linux GCC 10 Optimised (C++20)	4m 50s
Linux GCC 10 Debug (C++20) w/coroutines	5m 17s
Linux GCC 10 Optimised (C++20) w/coroutines	6m 5s
Linux Clang 10 Debug (C++17)	4m 3s
Linux Clang 10 Optimised (C++17)	5m 3s
Linux Clang 10 Debug (C++20)	4m 6s
Linux Clang 10 Optimised (C++20)	4m 51s
Linux Clang 11 Debug (C++17)	3m 25s
Linux Clang 11 Optimised (C++17)	4m 36s
Linux Clang 11 Debug (C++20)	4m 49s
Linux Clang 11 Optimised (C++20)	5m 44s
Linux Clang 12 Debug (C++17)	4m 14s
Linux Clang 12 Optimised (C++17)	4m 52s
Linux Clang 12 Debug (C++20)	4m 42s
Linux Clang 12 Optimised (C++20)	5m 13s
macOS GCC Debug (C++17)	3m 32s
macOS GCC Optimised (C++17)	2m 46s
macOS GCC Debug (C++20)	3m 44s
macOS GCC Optimised (C++20)	4m 24s
macOS Clang Debug (C++17)	3m 21s
macOS Clang Optimised (C++17)	3m 51s
macOS Clang Debug (C++20)	2m 23s
macOS Clang Optimised (C++20)	4m 23s
Windows MSVC 2019 Debug (C++17)	2m 6s
Windows MSVC 2019 Optimised (C++17)	1m 31s
Windows MSVC 2019 Debug (C++20)	5m 18s
Windows MSVC 2019 Optimised (C++20)	5m 36s
	2h 22m 2s

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