ICESat-2 tutorial link is broken

[asteiker]

This tutorial, under Tutorials / ICESat-2 is throwing a 404 error: https://nasa-openscapes.github.io/earthdata-cloud-cookbook/external/IS2_cloud_Landsat_integration.ipynb

This may be an issue with how this is linking to an external notebook in CryoCoud: https://book.cryointhecloud.com/tutorials/IS2_cloud_Landsat_integration.html

[andypbarrett]

Also see #223 and #221

[andypbarrett]

We need to have a process to decide when to link to an external notebook and when to copy. A decision point may be if the external resource is maintained and up to date.

Thoughts?

[cassienickles]

Also see #246

[andypbarrett]

Also see #268

[cassienickles]

created a PR #366