Feature/vault filter

[mindriot88]

• Adds the ability to limit requests make to the vault backend based on a key prefix.
• filter mode allows the given filter prefix to be stripped from the key prior to vault lookup.

The driver behind this change in my case was the volume of requests coming from class parameter lookups during each catalog compilation was slowing my puppet runs down and in some cases causing catalogs to fail to compile due to errors querying vault.

In my case I am using vault for only a limited sub set of secrets so exposing all hiera lookups to the vault wasn't necessary.

[ahmet2mir]

Any state on this PR ? @jsok ? Currently I must ignore via nginx reverse proxy ....

[pirxthepilot]

Any updates when this PR will be merged?