Add temp banner to advertise the Airborne & Field Data Workshop

[heidimok]

ADMG is holding a workshop in April. The team would like a temporary banner to promote this. It should be the same as then banner that was released for the non-beta release.

Acceptance criteria

• Yellow banner at the top of homepage
• Banner appears when you first navigate to site, but users are able to 'x' to close it
• Banner should be able to be easily removed after session
• Text:

Please join us online 23-24 April for the 2024 NASA Airborne & Field Data Workshop! For more information and to register (free), click here!

[heidimok]

https://github.com/NASA-IMPACT/admg-casei/pull/613#event-12172414591

[heidimok]

In staging: