adding feature flags

[kkchu791]

Fixes #2042

What changes did you make and why did you make them ?

Implementing posthog feature flags from backend to frontend. It's event driven architecture where a request is made to PostHog when client user refreshes.

1. Event Driven Approach (Chose this one because less complicated and we have small enough Daily Active Users where the client requests won't be an issue. If it does become an issue, we can try the second approach with SSE.)

2. Server Sent Events Approach ( Decided not to do this approach because the open connection adds complexity to the app which I don't think is needed. The benefits of this approach don't outweight the complexity it brings.)

Screenshots of Proposed Changes Of The Website