[Logstash] Document what are the files/paths to copy over to migrate an installation from a host to another

Users should not attempt to copy over different hosts Logstash files installed via a package manager (RPM/DEB).
They can copy the configuration files, the data folder and the location of files used by Logstash pipelines (e.g. sincedb files, dictionaries, JDBC Drivers, etc...). They might need to tweak file paths (if the destination host has different mounts or file locations).
They might need to re-apply some edits to the service files, the secret store, `jvm.options` overrides, etc...

If a migration across hosts is expected, then probably we might recommend using the `tar.gz` installation as it is somehow self-containes, as long as file paths are relative and no files are referenced outside the unpacked directory