feat(bigtable): introduce minimal DataConnection implementation #8469

Job	Run time
debug_job	3s
Save PR ref	3s
macOS-CMake	0s
Windows-CMake / cmake + msvc-2022 + x64 + Release + Core3	7m 47s
Windows-CMake / cmake + msvc-2022 + x64 + Release + Core4	13m 40s
Windows-Bazel	0s
macOS-Bazel	0s
Notify-Google-Chat	3s
	21m 36s

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