## Problem
part of https://github.com/neondatabase/neon/issues/11813
## Summary of changes
Add a lite PostHog client that only uses the local flag evaluation
functionality. Added a test case that parses an example feature flag and
gets the evaluation result.
TODO: support boolean flag, remote config; implement all operators in
PostHog.
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Signed-off-by: Alex Chi Z <chi@neon.tech>
