feat(sync): add umbrella header #7

Job	Run time
Sanitized Build and Tests (gcc, utils=OFF, net=OFF, json=OFF)	29s
Static Analysis	41s
Configuration Coverage	33s
Sanitized Build and Tests (clang, utils=OFF, net=OFF, json=OFF)	27s
Runtime Smoke Checks	31s
Standalone Package Export Check	26s
Valgrind Checks	33s
Sync Strict CI Summary	0s
	3m 40s

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