Replace GW target selection with TDE target selection

[jkrick]

Replace section 2 of the GW_host tutorial which finds a ra_center, dec_center, and radius_deg for a GW target with a TDE target.
Do this by grabbing TDEs from the transient input catalog used by OU. Use the example of how to interact with these SNANA parquet files from the SED_fit notebook. These notebooks should match in their approach and the way they talk about the catalog. This might not be so straightforward because not every healpix region will have a TDE, so we might need to find one that does. It doesn't matter which TDE we use, so we can just take the first one we find.

Also rename this notebook to be TDE_light_curve.md