Standardize engine metadata #176
Description
For context, please visit this pull request: Flagsmith/flagsmith-php-client#117
The goal of this issue is to update the metadata field name from flagsmith_id to just id, wherever it occurs.
This only affects the communication between the client and the engine, and has no influence on the evaluation product, so there is no urgency in this — only sheer motivation to make our implementation consistent across code bases, and the team aligned.