A 'Clamped' option for color-ramp definition with min-render/max-render boundaries

[jfbourgon]

min-render and max-render properties allow service administrators to define rendering boundaries for color-ramp definition. By default, values outside those boundaries are rendered as transparent pixels. For instance with the following configuration, any NDVI values above 0.5 or below -0.5 will be rendered as transparent.

type = "colorrampconf"
colors = ${color-ramps.ndvi}
min-render = -0.5
max-render = 0.5

It it might be interesting to offer to clamp values outside those ranges to color-ramp lowest/highest colors.