docs: generate sample code in the Java microgenerator (#392)

This PR was generated using Autosynth. 🌈

Synth log will be available here:
https://source.cloud.google.com/results/invocations/2eb44d9f-9230-443a-a6c3-d1d42a6b9d96/targets

- [ ] To automatically regenerate this PR, check this box.

PiperOrigin-RevId: 356341083
Source-Link: googleapis/googleapis@8d8c008