Add a collapse button on the left sidebar

[LouisGirones]

Is your feature request related to a problem? Please describe.
Nop, everything is fine

Describe the solution you'd like
I would like to be able to collapse the left sidebar, like it is done on gitlab. Or on other website I guess.

Exemple :

collapsed lesft sidebar :

not collapsed left sidebar :

Additional context
From what I saw, users rarely use this menu except for the admin(s) for whom there is a lot more of options. So a collapse button would just be nice for everyone.
Additionaly (but out of the scope of this feature request), it would be nice to be able to have a file tree in this left sidebar.

[wiswedel]

@Nextcloud/designers

[skjnldsv]

@jancborchardt, I think we had a talk about that years ago and we decided against it?

[jancborchardt]

This is basically a duplicate of #15831

• We could show the toggle button for the left sidebar always – which is discussed at Always show toggle for snap.js to hide appnavigation #15831
• The "Collapse" function you mention from GitLab is not something we will implement as it makes the navigation quite difficult to use – showing only icons as mystery meat navigation. I regularly have issues with it, don’t even want to imagine regular users.