ci: add run.sh to otel/distributed_tracing

[LeoRoccoBreedt]

Summary

• Adds run.sh for the OTel distributed tracing example
• Supports dry-run (no credentials) — prints trace tree locally
• Sends real traces to Opik when OPIK_API_KEY + OPIK_WORKSPACE are set; no extra OPIK_OTEL_ENDPOINT secret needed (defaults to Opik Cloud)

Test plan

• Ran locally in dry-run mode
• Ran locally with credentials — traces visible in Opik
• CI passed against lrb/ci-workflows

🤖 Generated with Claude Code

[fschlz]

Review against current main (PR #16 merged) — looks good, mergeable after a rebase.

Only adds run.sh (correct name, set -e + export OPIK_PROJECT_NAME ✓), no .github/docs churn, and both scripts support DRY_RUN — so the merged secrets-free dry-run job should pass.

Three quick confirms before merge:

1. git rebase origin/main (base moved since this was opened).
2. The merged lint job runs both ruff check . and ruff format --check . — confirm uv run ruff format --check . is clean, not just check.
3. cd integrations/otel/distributed_tracing && bash run.sh exits 0 with no credentials (the dry-run job), and logs traces with creds (the live-run job).