Problem Statement/Rationale

What is going wrong?
When background: true is specified as an option to aggregate, the mongosh shell swallows it and doesn't include it in the generated aggregate command that's sent to the server. This doesn't happen with the old mongo shell.

Steps to Reproduce

How could an engineer replicate the issue you’re reporting?
Run a command such as the following:

db.foo.aggregate([{ $out: { s3: { bucket: "david.golub", region: "us-east-1", filename: "bgtest", format: { name: "json" } } } }], { background: true })

Expected Results

What do you expect to happen?
The aggregate command sent to the server should include background: true.

Actual Results

What do you observe is happening?
The command sent to the server omits background: true.

Additional Notes

Any additional information that may be useful to include.