Implement read snapshot data logic

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 0% with 172 lines in your changes missing coverage. Please review.

Please upload report for BASE (baseline_resync@cf75abc). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
src/lib/homestore_backend/pg_blob_iterator.cpp	0.00%	139 Missing :warning:
...ib/homestore_backend/replication_state_machine.cpp	0.00%	28 Missing :warning:
src/lib/homestore_backend/replication_message.hpp	0.00%	5 Missing :warning:

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## baseline_resync #224 +/- ## ================================================== Coverage ? 56.74% ================================================== Files ? 32 Lines ? 1852 Branches ? 204 ================================================== Hits ? 1051 Misses ? 711 Partials ? 90 ```

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[xiaoxichen]

@koujl @JacksonYao287 pls take a review