Default AmpTable for AMP8I_PHS8I

[magelisk]

Currently, if SICD is provided with pixel type AMP8I_PHS8I, the code requires that AmpTable be provided. I believe that the code should provide a default AmpTable of just 0-255 instead of raiding a ValueError. SICD spec says:

If no amplitude look-up table is provided, pixel component AMP(row,col) is the pixel amplitude. Pixel amplitude AII(row,col) is determined as shown below. AMP(row,col), if AmpTable(0:255) is omitted