Simulation: Set stamp for fake `mower/status`

[rovo89]

Otherwise the timestamp is always zero, so all the updates are discarded in the monitoring node: https://github.com/ClemensElflein/open_mower_ros/blob/a71af5ac17547d4a93d30484779fd2606ab3bcd1/src/mower_logic/src/monitoring/monitoring.cpp#L71-L74

Due to that, battery voltage et al. are shown as 0 in the web app.

[ClemensElflein]

Thank you for the PR!