Add Spring 2023 showcase schedule

[paigem]

Adds those who have already been scheduled for the 2023 Pangeo Showcase

[github-actions[bot]]

Thank you for your contributions!

A preview of your changes can be viewed at:

• https://raw.githack.com/pangeo-data/pangeo/add-2023-showcase-preview/index.html

[paigem]

@JimColl It looks like you updated this file after I submitted this PR. However, this PR has more updated information.

@rsignell-usgs @JimColl I assume the best way forward is for me to cancel this PR and create a new one with the updated info?

[paigem]

Update: I'll push a new commit to build on top of the current showcase schedule page.