Updating the DMS oxidation chemistry

Based on previous laboratory studies, we expand the simplified DMS oxidation scheme used in CAM6-chem to capture the OH-addition pathway as well as the H-abstraction pathway and the associated isomerization branch.

The expanded DMS oxidation scheme has shown some important chemical and climate implications, which are detailed in this [recent paper](https://acp.copernicus.org/preprints/acp-2021-782/).

We would like to share our modified CAM6-chem codes with the community, which can be found [here](https://github.com/kamingfung/CAM/commit/84f298522a8c1dbe42620a9029c1c509ead19565?diff=split).

Summary of our code development:
- developed based on the codebase located in /glade/work/fvitt/cesm/cesm2.1.0_mosaic07/
- added API with MOSAIC and OASISS
- added expanded DMS oxidation scheme (both gas- and aqueous-phases)

Thank you in advance to @lkemmons and @fvitt for helping with reviewing our changes.