Generate mod_def.ww3 input file on the go

[ezhilsabareesh8]

This PR addresses part of issue #440 by implementing a feature to generate the mod_def.ww3 file on the go.

• Added functionality to generate mod_def.ww3 on the go.
• Updated the list of configuration files for WW3.

[pep8speaks]

Hello @ezhilsabareesh8! Thanks for opening this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file payu/models/cesm_cmeps.py:

Line 49:53: W291 trailing whitespace
Line 50:9: E124 closing bracket does not match visual indentation
Line 180:80: E501 line too long (89 > 79 characters)
Line 182:14: E114 indentation is not a multiple of four (comment)
Line 182:14: E117 over-indented (comment)
Line 183:14: E111 indentation is not a multiple of four
Line 183:14: E117 over-indented
Line 184:14: E111 indentation is not a multiple of four
Line 186:1: W293 blank line contains whitespace
Line 187:14: E114 indentation is not a multiple of four (comment)
Line 187:14: E303 too many blank lines (2)
Line 188:14: E111 indentation is not a multiple of four
Line 190:14: E114 indentation is not a multiple of four (comment)
Line 190:80: E501 line too long (83 > 79 characters)
Line 191:14: E111 indentation is not a multiple of four
Line 193:14: E114 indentation is not a multiple of four (comment)
Line 194:14: E111 indentation is not a multiple of four
Line 195:14: E111 indentation is not a multiple of four
Line 197:14: E114 indentation is not a multiple of four (comment)
Line 198:14: E111 indentation is not a multiple of four
Line 200:14: E114 indentation is not a multiple of four (comment)
Line 201:14: E111 indentation is not a multiple of four
Line 203:14: E111 indentation is not a multiple of four
Line 207:17: E117 over-indented