Collections: Create a collection with max_ttl

update: this MB covers create only, a separate MB tracks the ability to modify collection max_ttl (MB-31806)

To satisfy Collections product requirements a collection can define its own max-TTL (document maximum time to live). A collection that does not define a max-TTL will use the value from the bucket configuration string “max_ttl”.

A collection can have the TTL defined by adding the following entry to the collection entry structure (where n is a value).

“max_ttl”: n

Collection max_ttl behaves the same as the existing bucket max_ttl feature.

To correctly implement this feature we need.

1) Space in the VB::ManifestEntry to store the TTL and methods to get it from a CachingReadHandle
2) Wire it into the existing max TTL code (ideally, may not be possible unless we do many collection map lookups per set)
3) DCP needs to replicate the collection TTL as part of a DCP system event
4) If we support changes to the TTL we also need a new event which replicates collection config changes
4.5) The eraser code must drop these new events if the collection is dropped