Allow configurable exit code for the `crash` processor

[heikkilamarko]

Hi.

About the crash processor that was introduced in v4.47.0:
https://github.com/redpanda-data/connect/releases/tag/v4.47.0

Based on the current implementation, the exit code is always 1:
https://github.com/redpanda-data/benthos/blob/4cd5b09eff3eb816003c69323bbc54942883a1a3/internal/impl/pure/processor_crash.go

It would be nice to be able to specify the exit code as a field of this processor, similar to how you can do it with Go's standard library using os.Exit(code).

Also, consider adding some examples of the crash processor to the error handling documentation here:
https://docs.redpanda.com/redpanda-connect/configuration/error_handling/

[Jeffail]

Hey @heikkilamarko, we unfortunately can't add a new field to the new crash processor without it being a breaking change since it just takes a string field at the moment. However, we could add a new processor with a more explicit name like process_exit with the exit code as a field.

[heikkilamarko]

Adding the process_exit processor sounds great.