docs: Add pipeline lock examples

[mPokornyETM]

Summary

Add documentation examples for two common use cases.

Timeout inside lock (#740)

When timeout() wraps an entire pipeline or stage, the clock starts before the lock is acquired. Jobs that wait in the queue can time out before executing.

Solution: Place timeout() inside lock() — the countdown begins only after the resource is acquired.

Resource properties (#759)

Documents how resource properties (name:value pairs) are exposed as environment variables via the variable parameter, including naming patterns, filtering by properties, and common pitfalls.

Fixes #740
Fixes #759

[github-actions]

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