Allow blocking structured facts

[djuarezg]

This patch works as well for structured facts, not like #3998

This changeset adds two configuration options used by the facts PuppetDB indirector:

fact_names_blocklist
fact_names_blocklist_regex

They can be used to configure a list of fact names that will never be sent to PuppetDB, based on exact fact names or regular expressions.

This PR obsoletes: #3998

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