(maint) Sync TTL default values in the README with actual defaults
The TTL values from the readme do not correspond to those [configured by
the module](MOD) and are the [default values from PuppetDB](PDB).
Adjust the README so that it describes the actual configuration.
[MOD]: https://github.com/puppetlabs/puppetlabs-puppetdb/blob/11dc0dfd91b26e9babc31b0221cd2442ae1b46a9/manifests/params.pp#L40-L43
[PDB]: https://puppet.com/docs/puppetdb/latest/configure.html#node-ttl