Enhance the logic for determining quality flags for time summaries of point observations.

[JohnHalleyGotway]

Describe the Enhancement

While documenting MET's handling of quality flags for #2278, @JohnHalleyGotway found that that handling could be improved when computing time summaries of point observations. This step is preformed by calling common library code from the point pre-processing tools, including pb2nc, madis2nc, ascii2nc, and so on. As of MET version 11.0.0, the quality flag of the time summary observations is always stored by summary_obs.cc as being NA.

This issue is to enhance the time summary logic to provide more useful quality flag data.

MET supports the computation of several types of time summaries (min, max, range, mean, stdev, median, P##, sum). Recommend the following loigc:

• For min and max: Select the actual matching observation and report its quality flag string.
• For median, and P##: If the percentile corresponds to an actual observation, report its quality flag string. If its the average of 2 values, and those quality strings are numeric, report the maximum of their values.
• For the range: If the quality flags for the min/max are numeric, report the maximum of their values.
• For mean, stdev, and sum: If the quality flags are numeric, report the maximum of all values in the time window.

The question is what to do otherwise? If the quality flags are not numeric, should the output quality flag be "NA" or the most common string?

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