Add ability to import and export recordings

Having a recording with the right data can be very valuable when testing. Currently it seems there's a backup option that would technically do this, but it would also back up everything else in the DB and requires stopping the service to restore. And there's both the API and the CLI where I can see the recordings, but I can't export or download them. It would be nice to have this option on the API and/or CLI.

This is a bit similar to https://github.com/influxdata/kapacitor/issues/1348 but for recordings, and I didn't want to hijack that issue for this.

Start by reading the recording entry points in the API and CLI and compare them with the existing backup and restore behavior. Define a recording-only import/export path that does not require stopping the service; done means recordings can be exported and imported through the selected interface without backing up the rest of the database.

Written by the indexing model from the issue text.