(maint) Add puppetserver prune subcommand

[jcharaoui]

This adds a puppetserver subcommand to help garbage-collect old reports.

The default TTL is the same as the one used for PuppetDB (14d), where this garbage collection is done automatically.

[jcharaoui]

Related to: puppetlabs/puppet#9461

[jcharaoui]

I would happily write some documentation for this, however I can't seem to find where to push changes.

The file at documentation/README.md refers to https://github.com/puppetlabs/osp-docs but that project doesn't exist.

[jcharaoui]

Accompanying documentation bits for https://www.puppet.com/docs/puppet/8/server/subcommands :

prune

Deletes old files in reportdir or bucketdir. By default it deletes all files older than 14 days.

The first argument must be reportdir or bucketdir, and the second (optional) can be an age value.

Example:

puppetserver prune reportdir

Example:

puppetserver prune bucketdir 30d