[ENR-70] 🚀 Feature: Push updates for SDK cached feature flags values

[galkleinman]

🔖 Feature description

Implement push updates to feature flag values cached in the SDK memory.

🎤 Why is this feature needed ?

Currently, the update mechanism is based on polling with a given interval, it makes flag values stale till the next polling interval. In cases where freshness matters or cases where SDK on one machine triggers value updates and the rest are out of sync, using push updates will result in all machines being synchronized and near real-time freshness.

✌️ How do you aim to achieve this?

Make use of GraphQL subscriptions (WebSockets) to broadcast feature value changes to relevant (those of the tenant whose values have been changed) SDK instances.

🔄️ Additional Information

No response

👀 Have you spent some time to check if this feature request has been raised before?

• I checked and didn't find similar issue

Are you willing to submit PR?

None

_ENR-70

[tomer-friedman]

Implemented using graphQL Subscriptions over web-sockets. See 8c63067