dashboard: live log widget: add filter for severity

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• [x] I have read the contributing guide lines at https://github.com/opnsense/core/blob/master/CONTRIBUTING.md
• [x] I am convinced that my issue is new after having checked both open and closed issues at https://github.com/opnsense/core/issues?q=is%3Aissue

Is your feature request related to a problem? Please describe.

The old widget had an option for filtering the severity of shown messages, like in the normal log viewer. Please bring this function back.

Describe the solution you like

Settings for live log widget with an option to filter by severity.

Describe alternatives you considered

None.

Additional context

None.