Pipeline viewer: Add an option to disable/mask field names in conditionals

*Original comment by @suyograo:*

@bohyun-e brought up a good point today about security concerns around field names in the pipeline viewer. The only place I know that a field name or a config snippet is exposed is in the conditional UI component.


There could be customers who wouldn't want the field names shipped and exposed in the UI to all users. To this end, we should consider adding a granular config option (`xpack.monitoring.mask_field_names: true`) on x-pack-logstash to mask field names when shipping it.

I think the shape of the pipeline is still valuable with the masked conditional (at least the user knows there is a fork in the dataflow), so I'd prefer shipping `scrubbed` or some variation of it when this flag is allowed. I'd like to ship some value like `scrubbed` rather than skipping it entirely to differentiate this known scenario from any legit bug we have which would cause us to not ship data.

Thoughts?

/cc @acchen97 @bohyun-e @ycombinator @andrewvc