Deflake TestFluentForwardLog and TestTCPLog large payload query

[rafaelwestphal]

Description

Add short exact-match ID fields to the 250 KB test payloads in TestFluentForwardLog and TestTCPLog so Cloud Logging can index and retrieve the entries in < 1s without hitting the 20 KB query filter limit or suffering > 7.5m tail latency in the full-text substring indexer. Verify the 250 KB payload byte-for-byte in Go via gce.QueryLog.

Related issue

Bug: b/555757295

How has this been tested?

Checklist:

• Unit tests
  • Unit tests do not apply.
  • Unit tests have been added/modified and passed for this PR.
• Integration tests
  • Integration tests do not apply.
  • Integration tests have been added/modified and passed for this PR.
• Documentation
  • This PR introduces no user visible changes.
  • This PR introduces user visible changes and the corresponding documentation change has been made.
• Minor version bump
  • This PR introduces no new features.
  • This PR introduces new features, and there is a separate PR to bump the minor version since the last release already.
  • This PR bumps the version.

[LujieDuan]

LGTM!