datasets: don't allow absolute or paths with directory traversal

datasets: don't allow absolute or paths with directory traversal

For dataset filenames coming from rules, do not allow filenames that
are absolute or contain a directory traversal with "..". This prevents
datasets from escaping the define data-directory which may allow a bad
rule to overwrite any file that Suricata has permission to write to.

Add a new configuration option,
"datasets.rules.allow-absolute-filenames" to allow absolute filenames
in dataset rules. This will be a way to revert back to the pre 6.0.13
behavior where save/state rules could use any filename.

Ticket: #6118