[flagd] Implement basic Json Logic

[m-olko]

Because JsonLogic for C++ is not maintained and misses crucial for us features allowing for adding new operators (like fractional or starts_with), we need to implement our own. (Maybe share it as separate repo later on).
This task is aimed on creating basic JsonLogic here, without fractional or other advanced features.

The implementation should pass official tests.

[m-olko]

Currently this issue is on hold, waiting on discussion outcomes of open-feature/flagd#1848