Previously, BigDecimal was listed as not needing a serializer.  However,
when used with an adapter storing the job arguments as JSON, it would get
serialized as a simple String, resulting in deserialization also producing
a String (instead of a BigDecimal).

By using a serializer, we ensure the round trip is safe.

During upgrade deployments of applications with multiple replicas making use of
BigDecimal job arguments with a queue adapter serializing to JSON, there exists
a possible race condition, whereby a "new" replica enqueues a job with an
argument serialized using `BigDecimalSerializer`, and an "old" replica fails to
deserialize it (as it does not have `BigDecimalSerializer`).

Therefore, to ensure safe upgrades, serialization will not use
`BigDecimalSerializer` until `config.active_job.use_big_decimal_serializer` is
enabled, which can be done safely after successful deployment of Rails 7.1.

This option will be removed in Rails 7.2, when it will become the default.