gluon-authorized-keys: add unauthorized_keys to remove access

[mkg20001]

No description provided.

[mkg20001]

revoew discussion summarized:

• the unauthorized_keys feature in it's current state is not wanted
• the goal of authorized_keys was never meant to be a mechanism for rolling out keys

the reworked version:

• groups instead of main authorized keys, which are disabled by default (similar to ffda-ssh-manager)
• /etc/dropbear/authorized_keys -> /var/authorized_keys symlink, generate from /etc/config/authorized_keys? (persistent keys) and the enabled groups
• migration that moves /etc/dropbear/authorized_keys to persistent location and replaces it with symlink to generated version. generated version will also have read-only flag set.
• persistent additions to the persistent (!) authorized_keys file should still be possible via site.conf
• there should be a webui for the groups

[blocktrron]

I think this is a compromise in every aspect.

Over at freifunk-gluon/community-packages#24 we have a IMHO better solution to manage site-keys. This allows also to differentiate between site-originated keys as well as user-added SSH keys.

In my opinion, we can merge this and work towards integrating the community package into core-gluon, deprecating the current way of adding SSH keys using site-information.

[blocktrron]

Take note here that this will also remove SSH key which are originally added by the user.