[FSSDK-10553] add IsEveryoneElseVariation marker in decide API

[pulak-opti]

Summary

• added IsEveryoneElseVariation marker in decide API

Ticket

• FSSDK-10553

[mikechu-optimizely]

I read the Jira on this, but 2 initial thoughts:

1. Should this be solved in the SDK or via project configuration, as you mentioned as a variation?
2. If this is something that an SDK should handle, then perhaps it needs to be put in all the base language SDKs.

There's a high probability you've already run through all these thoughts, and I'm late to understanding.

I do not see any problems with the coded solution, but will refrain from providing Approval since I'm not fully knowledgeable on the problem.

cc @jaeopt

[pulak-opti]

Hey @mikechu-optimizely
Thanks for your thoughts. I have tried to implement this in the SDK first. You might have noticed the linked closed PR in SDK. But then I have changed my mind for the followings:

• User has requested the feature for the Agent
• Implementing this in SDK will force us to add this in other primary language SDKs to keep things in sync.
• Users can implement the same thing on their server side in the similar way as we have done it in Agent if they need it.

[jaeopt]

LGTM

[jaeopt]

@mikechu-optimizely @pulak-opti
I also see some value for adding this to all SDKs, hiding our naming rule for everyone-else.
The current implementation in agent looks reasonable for now and we can review it again for adding into the SDK level.