feat(podman): make container health check interval configurable

[sshnaidm]

Summary

Make the Podman driver's container health check interval configurable instead of hardcoded at 3 seconds. The short default spawns a conmon subprocess every tick per container, creating sustained process churn and unnecessary CPU overhead on systems running multiple sandboxes.

Related Issue

Closes #1832

Changes

• Add health_check_interval_secs field to PodmanComputeConfig (default: 10s)
• Wire the config value into the health check spec in build_container_spec()
• Backfill the new field via ..PodmanComputeConfig::default() in the standalone driver binary
• Document the new field in docs/reference/gateway-config.mdx

Testing

• mise run pre-commit passes (excluding pre-existing test:python grpc version mismatch)
• Unit tests added: default_config_sets_health_check_interval, container_spec_healthcheck_interval_from_config
• E2E tests added/updated (if applicable)
• Deployed patched binary locally, verified podman inspect shows configured interval

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)

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[sshnaidm]

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[TaylorMutch]

/ok to test 1d4d7ae

[github-actions]

Label test:e2e applied for 1d4d7ae. Open the existing run and click Re-run all jobs to execute with the label set. The run will execute the standard E2E suite after building the required gateway and supervisor images once. The matching required CI gate status on this PR will flip green automatically once the run finishes.

[TaylorMutch]

Can we validate the case for when the interval is set to 0?

Also this affects how quickly we check that the container is up and ready from the driver perspective; increasing to 10s doesn't seem like a lot but could be noticeable, I am okay with this change tho if we can validate the behavior when it's set to 0.

Thanks for the submission! If we can address my question above this LGTM