Improved UX when selecting and requiring permissions

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**Is your feature request related to a problem? Please describe.**
Users may choose to run the Nextcloud client with limited storage permissions. This may be useful if they only want to view files from a Nextcloud instance, but not upload any.

When first setting up the app, users are prompted to select one of two options, either allowing full read/write access, or media access only. If users do not grant any additional permissions, they may be prompted to grant certain permissions several times throughout the user experience; for example, when opening the "+" menu (floating action button) to create a new folder, an action that requires no additional permissions.

Users may also see options that actually require more permissions than the app currently has. For example, uploading files via the *Upload files* option in the "+" menu.

**Describe the solution you'd like**
During the onboarding process, users should be asked once whether they would like to set up any additional permissions. They should also be informed about the impact this will have on the overall user experience and the range of available features.

Personally, I would expect that features that are unavailable due to missing permissions to be hidden, such as the *Upload files* option. Hiding this option in this case would also reduce confusion, as users would still be able to upload files via *Upload content from other apps*.

In addition, I would not expect any requests to grant further permissions, especially when performing actions that do not require said permissions.

Finally, adding an option to the in-app settings menu to grant further permissions would be useful.

**Describe alternatives you've considered**
*Alternatives are to be discussed below.*

**Additional context**
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