Admin Panel: allow to filter the previous logs

[maximlt]

The Logs tab currently rely on the Terminal widget to show the logs emitted by Panel directly. It also offers widgets to filter the logs by sessions and components. However these widgets only affect the future logs, not the logs already recorded and streamed to the Terminal. In most cases I believe users will be interested in filtering previous logs, for instance to see what went wrong with a given session.

One way to improve the Logs tab would be to stream the logs to a Tabulator widget instead of to the Terminal widget, which could have columns such as timestamp, log level, session, component and message and activate header filters and sorters.