Record start/end/walltime in the wrapper script
Begin arcbot message
This merge request is automatically copied from !1399 (merged) orginally made by @andrii
End arcbot message
Small changes to process start/end and walltime recording to .diag
directly in the job wrapper script.
This helps to mitigate corner cases, where this info did not come from LRMS subsystem for whatever reason (e.g. BUGZ-4050).