Fix default gracedb_url
Sets the default url for gracedb_url to be https://gracedb.ligo.org/api/
Maintenance will be performed on git.ligo.org, containers.ligo.org, and docs.ligo.org on Tuesday 30 April 2024 starting at approximately 9am PDT. It is expected to take around twenty minutes and there will be several periods of downtime throughout the maintenance. Please address any comments, concerns, or questions to the helpdesk.
Sets the default url for gracedb_url to be https://gracedb.ligo.org/api/