introduce per-home dir overrides in afp.conf

[rdmark]

the [Homes] section in afp.conf currently support a small minority of configuration option overrides, and also the overrides uniformly apply to all home dirs

we should allow for optional overrides on a per user basis, e.g. user A opts into spotlight indexing of their home dir, while user B opts out of the same

at the same time, any option that is now a volume option should also be expanded to be applicable to a home dir

[rdmark]

quoting @andylemin

To provide per user override you would need the ability to optionally specify an individual [username] home mount with settings that override the common homes and global config. This would allow Spotlight to be enabled for only a single user if homes does not exist at all, or disabled if [homes] exists and enables.

[username] > [homes] > [global]

Whether you also allow those per username home mount settings to be defined in ~/.netatalk/afp.conf, IMO would just an extension of the same override logic.

However, only implementing the username override in the main afp.conf keeps it simple and focused on value (patterns that are most likely to actually be used = only settable by the admin).

And we still need to sort out Netatalk startup as non-root first.

So definitely keep it simple and only in the main afp.conf for now. Ideally we should allow any property under [homes] to be override-able. There are clear use cases for different permission bitmaps for example.