[TESTING] remove testbed sync-server in favor of flagd v0.9.1+

[toddbaert]

flagd itself now implements the sync.proto. This means the sync-server in this repo (only used for testing) can be replaced with flagd itself.

• [ ] update https://github.com/open-feature/flagd-testbed/blob/main/sync/Dockerfile and https://github.com/open-feature/flagd-testbed/blob/main/sync/Dockerfile.unstable to make use of flagd instead of the small implementation here
• [ ] delete https://github.com/open-feature/flagd-testbed/tree/main/sync/pkg

[aepfli]

do we actually need the sync docker files? seems like https://github.com/open-feature/flagd-testbed/blob/main/flagd/Dockerfile is already doing what we want. i think we can delete the sync folder, or am i wrong here. side question, do we need to somehow deprecate some artefacts? or are they somewhere used?

[toddbaert]

I think you're right @aepfli , we don't need another Dockerfile or image. I think we just need to expose a new port!