Feature Flags: Add Remote config to Java SDK

[phillram]

Feature request

Is your feature request related to a problem?

• Currently only the Node.js, Python, Go, Ruby, & C# SDK's can use Remote Configs.
• Java doesn't appear to have this functionality.

Describe the solution you'd like

• It would be great to add remote config to the Java SDK.

Describe alternatives you've considered

• At the moment you can construct flag calls for similar functionality, but this would be for parity.

Additional context

• From https://posthoghelp.zendesk.com/agent/tickets/60425

Debug info

Session: https://us.posthog.com/project/sTMFPsFhdP1Ssg/replay/019ecc7d-da51-798a-9dff-4036955dba94?t=17935
Admin (internal): http://go/adminOrgUS/019c4ed6-add0-0000-998a-30c999608349 (project ID 311650)

[marandaneto]

this is about the getRemoteConfigPayload method and not the /$token/config endpoint