Provide a client endpoint to trigger flag changes from outside the container, rather than trigger them periodically

[aepfli]

Currently, our testbed is changing a flag regularly to mimic flag changes and flag change events.
This works great, but it has the side effect that we regularly receive change events, which can lead to wrong results within the tests.
e.g. for the "InProcess," we currently have a bug where we are not moving from error to ready as long as there is no flag change event. So the e2e tests work due to the script.

Ideally, we would add a server with an endpoint where we can trigger this behaviour.

[aepfli]

i suggest to implement a HTTP server without bigger features (no ssl, no auth), i would suggest in go, which manipulates the flag configuration locally

[toddbaert]

If we're doing this, could we also have the server restart flagd itself so we can control the unstable tests this way?

[aepfli]

Sounds like a good idea, but I would start small and add this as a future improvement