nixos/nextcloud: make `profile.enabled` configurable
nixos/nextcloud: make `profile.enabled` configurable

I recently learned that Nextcloud 23's new profile feature — basically a
way for users to share personal contact details — has a problematic
default setting, profile data is shared with **everyone** by default.

This means that an unauthenticated user can access personal information
by accessing `nextcloud.tld/u/user.name`.

The announcement of v23 states[1]:

> We go a step further and introduce a profile page. Here you can put a
> description of yourself, show links to, for example, social media, what
> department you are in and information on how to contact you. All these
> are of course entirely optional and you can choose what is visible to who!
> The profile and user status are accessible also from our mobile and desktop clients.

It's not mentioned that by default you share personal information[3] with
everyone and personally I think that's somewhat problematic.

To work around that, I decided to add an option for the recently added[2]
and even set it to `false` by default to make an explicit opt-in for
that feature.

[1] https://nextcloud.com/blog/nextcloud-hub-2-brings-major-overhaul-introducing-nextcloud-office-p2p-backup-and-more/
[2] https://github.com/nextcloud/server/pull/31624/files
[3] By default, this affects the following properties:
    * About
    * Full name
    * Headline
    * Organisation
    * Profile picture
    * Role
    * Twitter
    * Website
    Phone, Address and Email are not affected and only shown to
    authenticated users by default.

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