[Bug]: Beam SDK is not visible to the backend code in SCIO

### What happened?

`GetMetadata()` endpoint introduced in #22542 is not able to return Beam SDK version for SCIO runners because it is not known during the container build time. Reason is that SCIO runners use [`spotify/scio-template.g8`](https://github.com/spotify/scio.g8) which has version 2.38.0 hardcoded.

It would be nice if we'd support:
- setting Beam SDK version during the container build
- having Beam SDK version visible to the backend so it will be possible to return in in `GetMetadata()`

### Issue Priority

Priority: 3 (minor)

### Issue Components

- [ ] Component: Python SDK
- [ ] Component: Java SDK
- [ ] Component: Go SDK
- [ ] Component: Typescript SDK
- [ ] Component: IO connector
- [ ] Component: Beam examples
- [X] Component: Beam playground
- [ ] Component: Beam katas
- [ ] Component: Website
- [ ] Component: Spark Runner
- [ ] Component: Flink Runner
- [ ] Component: Samza Runner
- [ ] Component: Twister2 Runner
- [ ] Component: Hazelcast Jet Runner
- [ ] Component: Google Cloud Dataflow Runner