Add submodule cobalt #42

Job	Run time
cmake-install-windows (windows-2019)	11m 44s
b2-windows (windows-2019)	37m 42s
b2-posix (ubuntu-20.04)	18m 41s
b2-windows (windows-2022)	37m 6s
cmake-install-windows (windows-2022)	12m 2s
cmake-install-posix (ubuntu-20.04)	3m 58s
b2-posix (ubuntu-22.04)	15m 42s
cmake-install-posix (ubuntu-22.04)	6m 20s
b2-posix (macos-11)	30m 14s
cmake-install-posix (macos-11)	8m 39s
b2-posix (macos-12)	18m 2s
cmake-test-windows (windows-2019)	30m 6s
b2-posix (macos-13)	22m 53s
cmake-install-posix (macos-12)	6m 54s
cmake-test-posix (ubuntu-20.04)	26m 0s
cmake-test-windows (windows-2022)	41m 49s
cmake-install-posix (macos-13)	11m 23s
cmake-test-posix (ubuntu-22.04)	33m 45s
cmake-test-posix (macos-11)	37m 18s
cmake-test-posix (macos-12)	35m 11s
cmake-test-posix (macos-13)	38m 19s
	8h 3m 48s

Provide feedback