Add COSMOS SEDs as additional template set #166

[sschmidt23]

Adds the COSMOS 30-band SEDs to the examples_data so users can easily run with a slightly expanded template set that is likely to perform better than the "default" CWWSB template set. I also included a prior file that uses the same HDFN parameters as the original BPZ prior, but with the appropriate numbers of SEDs per broad type for this set of 31 SEDs.

To go with this, I'll put in another PR to the rail repo to update the BPZ demo notebook so that it also runs this SED set and compares to the CWWSB set.

Code Quality

• My code follows the code style of this project
• I have written unit tests or justified all instances of #pragma: no cover; in the case of a bugfix, a new test that breaks as a result of the bug has been added
• My code contains relevant comments and necessary documentation for future maintainers; the change is reflected in applicable demos/tutorials (with output cleared!) and added/updated docstrings use the NumPy docstring format
• Any breaking changes, described above, are accompanied by backwards compatibility and deprecation warnings

[hangqianjun]

Looks good

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.35%. Comparing base (30a570f) to head (7e02a63).
Report is 3 commits behind head on main.

Additional details and impacted files

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##             main     #167   +/-   ##
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  Coverage   98.35%   98.35%           
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  Files          45       45           
  Lines        2497     2497           
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  Hits         2456     2456           
  Misses         41       41           

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