Output metadata should be updated to include start and end time from JobResult

[marcuscollins]

Right now, we write out metadata to a file job_metadata.json in the output directory, e.g.,
/data/sampleworks-exp/occ_sweep/grid_search_results_rf3_chiral_off/1VME_0.75occA_0.25occB/rf3_X-RAY_DIFFRACTION/pure_guidance/ens8_gw0.1/job_metadata.json. The data in this file is derived from the corresponding GuidanceConfig object, via its as_dict method. We should append this with other information in the JobResult object that is returned by the run_guidance method in guidance_script_utils.py, most importantly the start and end times of the trial.