[EDP] Allow editing of datasource objects

It's easy to make mistakes when specifying a data source, for instance when specifying a swift path or an absolute hdfs path. This will cause an error when the job is launched.

Currently, the recourse is to delete the old data source object and create a new one with the correct information and relaunch the job. It would be helpful if a user could simply edit the data source and correct the path in place, instead of deleting and creating.

This may have benefits in job relaunch, too, when a job execution references an existing data source (particularly in the case where a datasource is referenced by name or uuid in an argument list)