QC: Use gt for Report_MetricTable()

[jonthegeek]

QC Details

Report_MetricTable() uses kableExtra::kbl(), while Report_FlagOverTime() and Report_StudyInfo() use gt::gt() (via gsm_gt()). Update Report_MetricTable() to match.

Additional Comments

Note: Report_FormatFlag() will have to also be updated to output a format that gt() is compatible with (or potentially we need to do something to tell gt that the column contains SVGs).