Parameter conversion from STAC render extension to TiTiler

[StijnCaerts]

We are trying to use a custom colormap configured in the STAC render extension, following the color map JSON definition.
https://github.com/stac-extensions/render?tab=readme-ov-file#render-object

But this is not recognized in TiTiler because the validation of the colormap parameter is expecting a str instead of a dict.

I was able to fix this locally by dumping the JSON dict back into a str when constructing the LayerDict, but I don't know if this is the best solution.

titiler-stacapi/titiler/stacapi/factory.py

Lines 650 to 652 in aaf4249

	# TODO:
	# special encoding for ColorMaps
	render = layer["render"] or {}

# TODO:
# special encoding for ColorMaps
render = layer["render"] or {}
if "colormap" in render:
    render["colormap"] = json.dumps(render["colormap"])

[vincentsarago]

😓

titiler-stacapi/titiler/stacapi/factory.py

Lines 650 to 651 in aaf4249

	# TODO:
	# special encoding for ColorMaps

yeah I forgot to deal with this