xCDAT conversion: MJO and Monsoon Sperber

What's Changed

• Update sea ice figure script by @acordonez in #1097
• Handle NaN in sea ice clims by @acordonez in #1096
• MJO xcdat conversion by @lee1043 in #1091
• New monsoon sperber code in xCDAT -- PR cleaned up by @lee1043 in #1022

Full Changelog: v3.4.1...v3.5