[Proposal] Change permission in system logs

[catsmeatman]

Summary

System logs /manager/?a=system/logs is very useful thing. Now we have one permission 'logs' for two different action 'clear logs' and 'show logs'.

Why is it needed?

To have more powerfull and flexible permission roles.

Example.
There are 5 editor in online store. 4 editor - is simple editor who can't show logs and 1 chief-editor who can show logs, but not truncate it.

Suggested solutions

1. Add new permission 'clear_logs'
2. Permission 'logs' rename to 'show_logs'.

[Ibochkarev]

Update #15981