Write job metadata by default

[jmakeig]

When bulk loading data it’s helpful (and often required) to track metadata about the load itself. For example to identify a job by name, track the source system, etc.

DMSDK should add the job name as a metadata field for every update, including inserts and transformations. (The latter can be tricky in the case of updating multiple documents.) It must be possible for a user to override this to not insert any metadata or extend the default with her own.

Related tangentially to #441.

[jmakeig]

Related to #612.

[jmakeig]

Need to start with a how-to recipe on how you’d do this today and then later automate something out-of-the-box.

[ehennum]

Superseded by DHF.