Add support for flag metadata

[beeme1mr]

Requirements

Overview

The OpenFeature specification includes a concept called flag metadata. This is a great way to provide additional context in a flag evaluation. It's especially useful for troubleshooting and telemetry use cases.

Requirements

Tasks

Beta Give feedback

1. Update the flagd schema to include flag metadata flagd-schemas#174
   +0
   
2. Update flagd RCP and OFREP to support metadata
3. Update flagd providers to support flag metadata
4. Update flagd documentation to include flag metadata

Follow-up

Metadata at the flag set level would be useful for metadata that's shared across all flags (e.g. flag set version). This may require changes to the OpenFeature spec and SDKs to properly support.