(PUP-2995) Proposal for processing an external OID mapping file for
resolving custom trusted OIDs

This patch is a proposal that allows custom OIDs used in trusted facts to be resolved into user-friendly names that can be used in puppet manifests.

For instance a mapping file such as

```
---
oid_mapping:
  - ['1.3.6.1.4.1.34380.1.2.1.1', 'shortname', 'Long name']
  - ['1.3.6.1.4.1.34380.1.2.1.2', 'othershortname', 'Other Long name']
```

could be used to obtain `$trusted[extensions][shortname]`.

Before deciding to submit this proposal, we had written a custom puppet
function that does quite the same (`$mapped_trusted =
oid_to_name($trusted, '/etc/puppet/trusted_oid_mapping.yaml')`) but we
realize that other sites could need this feature.

_Note_: I couldn't achieve to add a configuration option for this as the
`puppet/ssl/oids` library seems to be loaded very early and I don't have
more time to dig deeper.