add feature to refine time range of metrics data

[harp-intel]

Is there a way to trim TMA metrics to a specific interval? Problem is sometimes we don't know when/how to consistently start and stop collection so end up collecting for the whole workload but then the aggregate values include setup and other parts of the workload we are not interested in analyzing.

Summary CSV and HTML reports are created from the metrics CSV report that contains metrics for all time stamps and the metadata collected. During a typical metrics data collection, without the --raw flag, the metadata is not retained. For this new feature we could start keeping the metadata in a file, like with --raw, or we could generate the summary without metadata. Note that the 2nd option means that the system summary data, which is part of the metadata also will not be present in the HTML report.

Need a way for user to signal perfspect that the intent is to trim down an existing report, likely through a command line argument.
Need a way for user to specify start and stop timestamps or time offsets.
Both the summary CSV and HTML reports should be produced in the same folder as the original.