[demo] - update to 1.12 release including new flagd UI

[klucsik]

For deploying https://github.com/open-telemetry/opentelemetry-demo/pull/1725. The flagd-ui needs to be in the smae container with flagd so they can share an emptydir volume which containes the jsonfile for flags. flgad-ui can write it, and flagd will pick it up instanly and distributes the new flag changes. I'm not very proficient with helm, please provide some input if this approach is fine or we can do this more neatly. I added just a object block for the schema, would be neater to validate the entire inner block, but this is well beyond my jsonschema understanding 😃