(#23074) Add reinventory command to puppet cert

This adds a reinventory command to the puppet cert application.

Further work on this is to refactor the use of the #apply method
found in Puppet::SSL::CertificateAuthority as it delegates to
a subclass called Interface to do the work. This is all an application
concern and it is confusing with the back and forth between the classes
"the cert application", the CA and its Interface.
(#23074) Add text to warn that master should be inactive for reinventory.
(#23074) Cleanup logic

This makes a couple of the methods in the CertificateAuthority and
related Interface classes easier to read / understand.
(#23074) Remove header in inventory.txt when regenerating

The regenerate inventory wrote a header that was not there in the
original file.
(#23074) Make cert inventory not rebuild inventory.txt when adding

There is a race condition that requires protection if the inventory
performs rebuild of a missing inventory.txt file when adding a cert.
Without the protection the inventory may end up with double entries or
missing entries, and with the protection the processing of cert requests
become serialized over all processors creating a performance problem.

This change simply appends to the inventory.txt - if the file does not
exists, it is atomically created.

A users that wants to recreate the inventory should do so with the
command `puppet cert reinventory` which may be executed on an
inactive system.
(#23074) Refactor cert application's use of cert authority's interface

The code was difficult to understand as the cert application called
the apply function on the CertAuthority, which in turned created an
instance of the Interface class, which in turn called back into the
ca. As this construct was only used by the cert application, the ca's
apply method was moved to the cert application.

It is now more clear that the application interacts with the ca via
an instance of its Interface class.
(#23074) Remove overly stubbed tests

There were several tests attempting to test the cert application,
the CertificateAuthority and its interface, as well as the inventory
handling by use of excessive stubbing that prevents any real code from
being tested.

The failing overly mocked tests have been removed. Their value was
questionable to begin with.
(Maint) Small cleanups

Just a simple typo fix and re-expanding some blocks to make adding in
debugging easier at a later date.(Maint) Small cleanups
Merge branch 'hlindberg-feature/master/allow-rebuild-of-inventory'

* hlindberg-feature/master/allow-rebuild-of-inventory:
  (Maint) Small cleanups
  (#23074) Remove overly stubbed tests
  (#23074) Refactor cert application's use of cert authority's interface
  (#23074) Make cert inventory not rebuild inventory.txt when adding
  (#23074) Remove header in inventory.txt when regenerating
  (#23074) Cleanup logic
  (#23074) Add text to warn that master should be inactive for reinventory.
  (#23074) Add reinventory command to puppet cert

Closes GH-2032