Provide endpoint to monitor progress of an export-job

[kschulst]

The users should be able to query the API and get back information about ongoing export jobs, such as:

• stauts (in progress, done, failed, ...)
• Target path
• Username that triggered the job
• some metrics (number of processed records ++)
• any error messages

It should be possible to filter the list of jobs by status (e.g. to only see failed jobs)

[kschulst]

Possible approach:

• Introduce some kind of ID associated with a job
• Use an in memory map or database to keep track of jobs (can later be save e.g. to a volume or database)