[CBM] Split the collection manifest out to the vBucket level

What's the issue?
The collection manifest needs to be "split" out to the vBucket level, where we can then use DCP stream events to capture/track the "range" or "lifetime" of scopes/collections.

What's the fix?
We should use the "base" manifest (fetched via 'ns_server') as a starting point for each vBucket.

During DCP streaming, we'll use scope/collection create/delete events to add "range" or "lifetime" information to a scope/collection in the manifest.

We will also need to track/create tombstones for scopes/collections that have been dropped; we must be able to fetch the name (otherwise the scope/collection is unusable).