Add reference of colormaps

[ldr426]

Change name of colormap from color_map to colormap.

Hard to know if one needs to type in, and what colormap options are.

• Add an option to have a drop down menu with a few popular colormaps and then Other option in which to type an extra colormap.
• Add a link to colormaps.

_Originally posted by @valentina-s in https://github.com/OSOceanAcoustics/echoshader/pull/93#discussion_r1231235507_

[ldr426]

Has been added in python docstring