Add submodule mqtt5 #3349

Job	Run time
b2-windows (windows-2019)	31m 11s
b2-posix (ubuntu-20.04)	14m 34s
cmake-install-posix (ubuntu-20.04)	4m 54s
b2-posix (ubuntu-22.04)	13m 35s
b2-posix (ubuntu-22.04-arm)	14m 13s
cmake-install-posix (ubuntu-22.04)	4m 56s
b2-windows (windows-2022)	31m 6s
cmake-install-posix (ubuntu-22.04-arm)	5m 27s
b2-windows (windows-2025)	31m 21s
cmake-install-posix (ubuntu-24.04)	4m 48s
b2-posix (ubuntu-24.04)	12m 33s
cmake-install-windows (windows-2019)	9m 13s
b2-posix (ubuntu-24.04-arm)	14m 28s
cmake-test-posix (ubuntu-latest)	56m 12s
cmake-install-posix (ubuntu-24.04-arm)	6m 21s
cmake-install-windows (windows-2022)	9m 32s
cmake-install-windows (windows-2025)	10m 28s
b2-posix (macos-13)	26m 23s
cmake-install-posix (macos-13)	10m 8s
b2-posix (macos-14)	11m 5s
cmake-install-posix (macos-14)	6m 43s
cmake-test-posix-quick (ubuntu-20.04)	3m 45s
b2-posix (macos-15)	11m 35s
cmake-install-posix (macos-15)	7m 9s
cmake-test-posix-quick (ubuntu-22.04)	2m 22s
cmake-test-posix-quick (ubuntu-22.04-arm)	2m 49s
cmake-test-windows-quick (windows-2019)	6m 50s
cmake-test-posix-quick (ubuntu-24.04)	2m 21s
cmake-test-windows-quick (windows-2022)	5m 50s
cmake-test-posix-quick (ubuntu-24.04-arm)	3m 3s
cmake-test-windows-quick (windows-2025)	5m 51s
cmake-test-posix-quick (macos-13)	8m 32s
cmake-test-posix-quick (macos-14)	4m 19s
cmake-test-posix-quick (macos-15)	6m 24s
	6h 40m 1s

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