Lagrangian remapping algorithm code

[chrisb13]

This PR is a placeholder to add notes for @KKukreja-code session on

the Lagrangian remapping algorithm in the MOM6 source code, specifically the creation of the subgrid from the source and target grids, the polynomial reconstruction of tracer values on the source grid to find concentrations in target cells, and how the code enforces conservation of tracer content and checks it. 

To add content, just edit this file on this branch (kkukreja/remapping-code):

• documentation/docs/pages/mom6/vertical-lagrangian-remapping-code.md

The PR then makes a rendered version of the site, which you can view here (once you push to the branch/pr).

FYI, happy to review things if useful but note that reviews on this repo' are optional.

@KKukreja-code, once done, please add your authorship details here:

• https://github.com/ACCESS-Community-Hub/decoding-om3/blob/main/CITATION.cff
• https://github.com/ACCESS-Community-Hub/decoding-om3/blob/main/documentation/docs/pages/index.md

[chrisb13]

Thanks very much @KKukreja-code! Merging as requested.