Queue Background operations

Problem

Create BBO models (!203234 - merged) added the schema for background operations and this issue provides helper to enqueue operations in it.

Background operations can be enqueued by two ways,

1. User action: This is org specific and these operations will be added to background_operation_workers table.
2. Cronjob: This is instance wide and are not associated to a org, these will be added to batched_operation_workers_cell_local table.

This will add a class method on worker models to enqueue new records, will also ensure that no duplicate entries are allowed.

Reference:

Here an our existing helper for BBM.