SoC Timestamp support for openWB

[tosate]

Fix for Issue #378: Add support for soc_timestamp topic for openWB

[nanomad]

Hi @tosate, thanks for this PR! Could you rebase it onto the latest main branch? It's currently showing conflicts.

Also, one issue found during review:

SoC timestamp published even when SoC is None
The timestamp block at the end of update_openwb runs independently of whether SoC was actually published. If soc is None, openWB would still receive a fresh timestamp, misleading it into thinking the SoC was just updated. The fix is to nest the timestamp publishing inside the existing if soc is not None and soc_topic is not None guard.

Thanks!