Add COSMOS SEDs to SED folder for alternate to CWWSB set

[sschmidt23]

LePhare demo uses the 31 SEDs used to compute the COSMOS 30-band photo-z's, consisting of empirical Elliptical and Spiral templates, plus some BC03 models. It would be good to have these included in RAIL, as they may produce better results than the smaller, older CWWSB template. Set. In addition to adding the SEDs and a file with some documentation, I'll also add a note in the rail_bpz repo and add a demo on the BPZ rail example notebook in those repos.

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