Ability to specify lifespan for AtomicMaps through AtomicMapLookup API

Currently there is no way to specify the lifespan of an AtomicMap when it is created through AtomicMapLookup.
Some overloads of AtomicMapLookup#getAtomicMap() and AtomicMapLookup#getFineGrainedAtomicMap() should be provided that take the (..., long lifespan, TimeUnit unit) extra parameters.

See the forum reference for a workaround.