Re: [PATCH v3 02/17] object-store: rename `object_directory` to `odb_alternate`

> The `object_directory` structure is used as an access point for a single
> object directory like ".git/objects". While the structure isn't yet
> fully self-contained, the intent is for it to eventually contain all
> information required to access objects in one specific location.
> 
> While the name "object directory" is a good fit for now, this will
> change over time as we continue with the agenda to make pluggable object
> databases a thing. Eventually, objects may not be accessed via any kind
> of directory at all anymore, but they could instead be backed by any
> kind of durable storage mechanism. While it seems quite far-fetched for
> now, it is thinkable that eventually this might even be some form of a
> database, for example.
> 
> As such, the current name of this structure will become worse over time
> as we evolve into the direction of pluggable ODBs. Immediate next steps
> will start to carve out proper self-contained object directories, which
> requires us to pass in these object directories as parameters. Based on
> our modern naming schema this means that those functions should then be
> named after their subsystem, which means that we would start to bake the
> current name into the codebase more and more.
> 
> Let's preempt this by renaming the structure to `odb_alternate` now
> already. This name is agnostic of how exactly objects are stored while
> still specifically pinpointing that this is about an alternate object
> database. Furthermore, it is already used in Git to represent this
> context -- the only stretch is that the primary object directory is now
> the primary alternate.