Issue Description

Since #1155 we have the ability to configure background_worker_threads which currently defaults to `Concurrent.processor_count. However, this config is likely to be too high in a shared hosting environment, leading to unnecessary memory usage. It may make sense to change the default to, say, a static 1 or 3 and add documentation about how best to configure?

See also: https://github.com/rails/rails/pull/50669/files#diff-e25cab4832f078ca2f9dffa8918f895c8474f8086878e4ced9f5795131fc2de2R32

/cc @st0012

Feel free to disregard, since this is easy to correct, but in my case I was surprised at the impact lowering from 8 to 1 made on my memory use on Heroku.

Reproduction Steps

$ heroku run rails c
Running rails c on ⬢ APP_NAME... up, run.4033 (Standard-1X)
Loading production environment (Rails 7.1.3.2)
irb(main):001> Concurrent.processor_count
=> 8

Expected Behavior

Consider defaulting to a static/lower number of background_worker_threads.

Actual Behavior

Defaults to Concurrent.processor_count.

Ruby Version

3.3.3

SDK Version

5.17.3

Integration and Its Version

No response

Sentry Config

No response