(feature) Add toggle to allow auto-scroll forward of dagu logs

[zph]

It would be a pleasant feature to be able to toggle the current behavior for logs (no auto-scrolling) with auto-scrolling on the execution view of logs.

I'm not sure about the implementation so I'm mostly posting to see if this is a desireable feature in the project outside of my own wishes. Then based on response I can determine if I want to look into fixing.

I think it's a mild nice-to-have feature :) but not highly important b/c user can manually try scrolling.