[EDP] Add options supporting DataSource identifiers in job_configs

In some cases it would be convenient if users had a way to pass a DataSource
object as a job configuration value to take advantage of the data codified in
the object instead of copying and specifying that information manually.  This
specification describes options that allow users to reference DataSource
objects in configuration values, parameters, and arguments in a JobExecution
record.

blueprint edp-data-sources-in-job-configs

Change-Id: Ib07e667e019c0002fe11ac1889751844e7435bd6
Merge "[EDP] Add options supporting DataSource identifiers in job_configs"