Allow inputs to automatically clean fields

## What?

Graylog disallows message fields that do not adhere to a specific pattern: https://github.com/Graylog2/graylog2-server/blob/496233da162a439a1e1cb6b63b6485bad7720c5a/graylog2-server/src/main/java/org/graylog2/plugin/Message.java#L219

When a user sets/creates fields, such as via a pipeline and using `set_field` or set_fields` they have access to the `clean_fields` argument.

However, when using some inputs, such as beats, the user cannot control how fields are delivered to the graylog input.

This issue is asking to have a checkbox, configured on the input's configuration page, that, when enabled, will do the same thing that `clean_fields` does.

## Why?

The user does not have the ability to correct invalid field names that arrive to the graylog input already invalid.