Update `cadir` default to return the new location post-migration

In order to make the transition to the new CA dir location as seamless as possible, we want to put some special logic into the default calculation for the cadir setting in Puppet, that will make it return the new location after the CA has been migrated, and warn otherwise.

If the setting is not configured by the user (default, use a Ruby lambda/proc):

• and the files are in the old default spot, warn with a message that encourages users to migrate. Return the old default (/etc/puppetlabs/puppet/ssl/ca)
• and there are no CA files (new install) or CA files in the new location, return the new location (/etc/puppetlabs/puppetserver/ca).

If the setting is configured by the user (custom, use hook (example)):

• and points to a location within the SSL dir, warn with a message that encourages migration
• and points to a location outside the SSL dir, use it as-is.