This adds support to display vertices lines over the profile graph to
display indicator at the location of the vertices of the trace.
This is mainly achieved by adding
`QgsElevationProfileCanvas::setSubsectionsSymbol()`. This method
allows to set the line symbol of the vertical lines. Then, It sets the
subsections symbol of the profile renderer of the plot item. It the
renderer does not exist yet, the subsections symbol is set when a new
profile renderer is created.
If checked, this option reverse the slider in the elevation filter
so that the widget goes from high values at the bottom to low values at the top.
See justification in https://github.com/qgis/QGIS/issues/56995Fixes#56995
