API: Create a batch operation

[srindom]

Creates a batch operation. The type of batch operation determines what should be included in the context. If the batch job is created with dry_run: true final confirmation through /batch/:id/complete will be required before the final data is uploaded to the DB.

POST /admin/batch

Body
- type
- context
- dry_run - true/false
- (potentially a location for a import file)

Response
- batch_job - { id, status ... }

DoD

• Endpoint should create new BatchJob - the new BatchJob's created_by field should correspond to the authenticated user
• Endpoint controller should call the *Strategy.validateContext method (this should be done through the BatchJobService)
• Endpoint should respond with the created BatchJob

[olivermrbl]

Solved in #1387