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

[klucsik]

For deploying open-telemetry/opentelemetry-demo#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 😃

[puckpuck]

@klucsik I updated your branch to work in a way that feels more natural with the rest of how the demo is setup.

This changes to using an array for the sidecarContainers property. It also adds a new property called additionalVolumes at the component level, which can be used to define volumes referenced from any of the pod's container volume mounts. I also removed some schema restrictions around defining both init and sidecar containers.

[puckpuck]

I can install the chart in this PR. I can also run ct against it locally on my system and it works just fine, but our CI tests are failing. I could use some help to understand why our CI fails in GHA but not locally.

The differences I can see are:

• helm version (3.16.2 locally vs 3.9.4 in GHA)
• ct version (3.11.0 locally vs 3.10.1 in GHA)
• environment (MacOS locally vs Linux in GHA)

[TylerHelmuth]

I can help investigate this week

[TylerHelmuth]

I believe the issue is using tpl inside range: helm/helm#5979. @puckpuck @klucsik can you update the Setup step in .github/workflows/lint.yaml and .github/workflows/demo-test.yaml to use helm 3.14.4

[TylerHelmuth]

@puckpuck I'll wait to merge until you approve