Separate worker and insertion of jobs. about river

[brandur]

@brycegoh Yeah, it's a bit hard to find, but the docs for this are in the Config section:

	// Queues is a list of queue names for this client to operate on along with
	// configuration for the queue like the maximum number of workers to run for
	// each queue.
	//
	// This field may be omitted for a program that's only queueing jobs rather
	// than working them. If it's specified, then Workers must also be given.
	Queues map[[string](https://pkg.go.dev/builtin#string)][QueueConfig](https://pkg.go.dev/github.com/riverqueue/river#QueueConfig)

So omitting the Queues configuration property makes the client insert only. You can technically omit the Workers property as well (where jobs are configured), but we recommend leaving this in because if it's present, the River client will verify at insertion that a job is properly registered with a corresponding worker that can process it.