[flagd] Update in-process resolver to support flag metadata

[toddbaert]

With this schema change, flag metadata can now be stored in flag configuration files. Specifically, these can contain things like version and flag set id information so that consumers can use this data in flag evaluations, caching, telemetry etc.

We need to add this metadata into flags which are evaluated by in-process resolvers. Essentially, we need to take the new properties from the flag definition and include them in metadata returned in the flag resolution.

Acceptance criteria:

• metadata defined in flag configuration (specifically id and version) are returned from any flag resolved from this set
• associated tests