cbstat allocator is moved to mcstat

The cbstat allocator command no longer works on 7.0, allocator stats are actually process global and not associated with a bucket, they are now available in mcstat and do not require a bucket argument.

E.g. the following no longer applies to 7.0
https://docs.couchbase.com/server/current/cli/cbstats/cbstats-allocator.html

7.0 release note should also document this change.

Note I cannot see any docs for mcstat?