fine tune the save button layout in settings page

[a110605]

Goal

Fine tune the save button layout in settings page to make it significant visible in any browser zoom ratio or small screen.

Issue

https://github.com/longhorn/longhorn/issues/7497

My previous PR sticky the save button at the buttom of page.

But it will be unvisible if user zoom into bigger browser ratio (e.g. 100%). This PR makes button all visible to any zoom ratio.

Test Result

zoom out to 67%

Zoom in to 133%

In small screen