Add option to redact args in stacktraces

[mattbaker]

We'd like an option to redact arguments in stacktraces before the stacktraces are sent to New Relic.

This draft currently adds a configuration value that will replace arguments in a stacktrace with the string "DISABLED arity: ($X")

It's a work in progress.

TODO:

• Tests to verify args are redacted in all the ways stacktraces can leave the agent for New Relic