[Task]: Examples for the Playground Frontend integration tests

### What needs to happen?

In the Playground database we need to have examples that integration tests can load. To be reliable, these examples should not be changed or deletable by Apache Beam editors.

Examples should be on both staged/deployed backend and local backend that is started with
`./gradlew :playground:dockerComposeLocalUp`

The source code of these examples should be structured in the directory tree so that new examples can be easily added in the same or other SDKs. Adding examples may require changes in the CI/CD code, but changing an example's should not require changing CI/CD code.

Each of such example's output should be ` output`.
Each of such example's logs should be ` log`.

So far we need only one such example in Go. Its code is here: https://github.com/akvelon/beam/blob/issue24959_test-loading-url/playground/frontend/playground_components_dev/lib/src/examples/content/example.go
It can be placed and/or renamed as is convenient.

Suggested path to fetch it:
`SDK_GO/INTEGRATION_TEST/Example`

### Issue Priority

Priority: 3 (nice-to-have improvement)

### 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

Start with the Go example at playground/frontend/playground_components_dev/lib/src/examples/content/example.go and inspect the local backend command ./gradlew :playground:dockerComposeLocalUp. Add a structured example available through SDK_GO/INTEGRATION_TEST/Example in both local and staged/deployed backends, protected from editing or deletion, with the specified output and log text.

Written by the indexing model from the issue text.