Update ports_purge docs and definitions

[KayckMatias]

This PR is reference to issue #14336
The cron worked so that it validated if the ports definition was true or false, but in the documentation and in the configuration it was as int of days, so I changed it to boolean and updated the documentation.

Before:

After:

DO NOT DELETE THE UNDERLYING TEXT

Please note

Please read this information carefully. You can run ./lnms dev:check to check your code before submitting.

• Have you followed our code guidelines?
• If my Pull Request does some changes/fixes/enhancements in the WebUI, I have inserted a screenshot of it.
• If my Pull Request makes discovery/polling/yaml changes, I have added/updated test data.

Testers

If you would like to test this pull request then please run: ./scripts/github-apply <pr_id>, i.e ./scripts/github-apply 5926
After you are done testing, you can remove the changes with ./scripts/github-remove. If there are schema changes, you can ask on discord how to revert.

[PipoCanaja]

LGTM