The plot plugin is very useful for tracking multiple build/app/test metrics, but
occasionally when things go wrong an unusally large metric value reduces the
utility of the plot since the plot scales the y-axis based on the maximum value.
The workaround would require manually editing/deleting/rebuilding metrics which
in not really tenable.

So an extremely helpful enhancement would be to enable the plot config to also
accept option minimum and maximum y-axis scale values to override the current
(default) mechanism of using the maximum value of the metric to set the upper-bound.

Since 0 is currently always the lower-bound, the ability to specify a different
absolute lower-bound would enable certain plots to be much more readable as a
result of better using the plot space and making smaller relative changes much
easier to see.

For metric values that fall above/below the custom y-axis boundaries, preferably
a * would be displayed on the top/bottom of the plot window for that build and
mouse-over would reveal the actual value (as current mouse-over of plot points
does), to enable determination of actual extreme values when needed.

Also the custom y-axis bounds should not lose any metric values (data), so if at
a later point in time the bounds are changed to a different range there would be
no data loss due to the earlier customized settings for the y-axis bounds.