fix #4442: Add date-time filtering for firewall logs

fix #4442: Add date-time filtering for firewall logs

Extend the current firewall log view to add date time based filtering.
The user can switch between live view, which shows logs from the
unrotated log file, or to filter mode, where date time based filtering,
including rotated logs can be performed.

Enable the feature by setting the property and the submit format
for since and until timestamps expected by the api.

Signed-off-by: Christian Ebner <c.ebner@proxmox.com>