Nextcloud icons should be updated and made available for local usage

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## Feature request

**Which Nextcloud Version are you currently using:**
Nextcloud desktop client 3.15.3
macOS Sequoia 15.2 (24C101)

**Is your feature request related to a problem? Please describe.**
Difficult to identify Nextcloud amid other Finder and menu bar icons, similar to what has already been [previously described](https://help.nextcloud.com/t/os-x-client-icon-is-very-awful/24449/3).

**Describe the solution you'd like.**
The current set up of NextCloud folder location does not conform to other cloud providers in macOS. The folder can be synced with any folder in the computer, instead of being allocated to `~/Library/CloudStorage/` by default.

I personally like this, as it grants me more freedom, but at the same time the choice of not automatically changing the folder icon makes the directory not clearly stand-out as a cloud sync, _i.e._ it can be mistaken for a local directory.

I have placed the NextCloud folder in the path above:

but nevertheless changed the folder icon to the one that can be found in the app's `Contents/Resources` folder, as a temporary solution for my own usage:

As it can be seen from the last image, I have also changed the icon of a different NextCloud folder (from a guest account, that uses a private email instead of my enterprise one) using an _ad hoc_ icon I [found online](https://www.deviantart.com/sc20k1/art/Nextcloud-Icon-769099229), even though it does not conform to the style of the current macOS version. This attempts to match the procedure adopted by Synology, in which the main cloud folder has the app icon, but a "SHARED WITH ME" folder (similar to that of a guest user) has a normal folder icon with a recessed logo (see above, as well).

This issue is also somewhat extended to the menu bar icon, which does not distinguish itself from other icons as "the nextcloud one". As one can see below, it is difficult to find nextcloud since its icon looks like a standard notification check-mark, instead of the nextcloud logo. A better approach would be the one taken by other companies, that use the logo as an icon and modify it with small additions such as "syncing" or "completed" symbols on the lower-right or lower-left corners (_e.g._ dropbox notifications, in this image).

**Alternatives you've considered.**
To avoid forcing a procedure on all users, the `Contents/Resources` folder in the MEGAsync app makes all `.icns` files from previous macOS versions available, so each one can potentially chose to save and apply it themselves:

Nextcloud could just do something similar and make all icons available.

**Additional context**
None

Start by inspecting the macOS app bundle's Contents/Resources folder and the existing Finder folder and menu bar icon assets. Determine which current assets represent sync states and which additional icons should be exposed for local use. Done means the requested macOS icons are updated or available as described and the Finder and menu bar representations are distinguishable.

Written by the indexing model from the issue text.