Provide a way to temporarily hide "custom patch" panel

[OliverJAsh]

Is your feature request related to a problem? Please describe.
When I am selecting lines/chunks to add to a patch, I have this problem where it is difficult to see the full code I am selecting because the "custom patch" panel is taking up too much space. For example, here I have a chunk selected, but I have to scroll to see the full chunk:

Describe the solution you'd like
I would prefer a workflow where I'm focused on selecting lines/chunks and then, when I'm done, switching to another view which just shows the custom patch. This is similar to what I would do outside of lazygit—I would run git add --patch and then, when I'm done, run git diff --cached to review the staged patch before committing. If I need to make more changes I can jump back to git add --patch.

Describe alternatives you've considered

Additional context
#749 would also help with this

[jesseduffield]

You can get halfway there by tapping '+' until the currently focused panel takes up the whole screen, however at the moment it's not possible to focus the secondary panel. I'll need to add support for that

[veremenko-y]

I would love this as well. I generally want to preview changes before doing selection to stage, and I have to press + twice until the 3rd view, then same + twice to get out of it.

[veremenko-y]

As an alternative, what about hiding "Staged changes" and "Custom patch" windows until there's something selected.