Fix unintentionally scrolling sidebar

[timrspratt]

When using certain field components that have <template> tags in for modals and alpine collapse functionality, the sidebar can end up scrolling incorrectly over the sticky header.

The header is sticky with a z-20, so this PR adds the same to the sidebar.

Top header wrapper:

Sidebar wrapper before:

Sidebar wrapper after:

Video showing issue:

https://github.com/filamentphp/filament/assets/20431294/5da54f86-a5fc-4143-a755-f7dfee818192

I have checked scenarios for mobile menu, top navigation, collapse navigation and all appear to be correct.

[timrspratt]

I'll have a play with fixed properly when I can. A quick try just now and it looks like w-full would also be needed.

[zepfietje]

Are you able to pick this up again, @timrspratt?

[zepfietje]

I'm going to close this PR, since there hasn't been any activity and requires some more testing before it can be merged.

Feel free to open a new PR when you've had a chance to look at my change request, @timrspratt. 🙂