Self-contained examples (no internal GFDL paths)

[hdrake]

The cross-section transport examples, e.g. OSNAP_CM4p125.ipynb, currently use internal GFDL paths to /archive/. For better accessibility to the broader ocean modeling community, we should either link to existing publicly available diagnostics or upload our own sub-sampled ones directly in this repository, as done for the grid file grid_CM2_minimal.nc.

[hdrake]

See related discussion in https://github.com/raphaeldussin/sectionate/pull/19/files/550aa7c674329decb676d2830852bc197bafae5f#r1294543046

[hdrake]

Should eventually make more data publicly available, but for now it suffices for the first example to be doable with the minimal data file that lives in the repo. All of the other examples should be accessible to anyone who can access GFDL paths.