feat(sync): add umbrella header #8

Job	Run time
Sanitized Build and Tests (gcc, utils=OFF, net=OFF, json=OFF)	32s
Runtime Smoke Checks	25s
Configuration Coverage	25s
Static Analysis	28s
Valgrind Checks	26s
Standalone Package Export Check	25s
Sanitized Build and Tests (clang, utils=OFF, net=OFF, json=OFF)	28s
Sync Strict CI Summary	0s
	3m 9s

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