Partition feature flag

[garrensmith]

Overview

Add partition feature flag based for #1789

Testing recommendations

Create something like this in local.ini:

[feature_flags]
partitions||* = false
partitions||allowed* = true

Then:
curl -X PUT http://localhost:5984/not-allowed?partitioned=true should throw an error
curl -X PUT http://localhost:5984/allowed-partition?partitioned=true should be created

Related Issues or Pull Requests

#1789

Checklist

• Code is written and works correctly;
• Tests

[iilyak]

+1

[davisp]

Whoops. PRs into PRs are weird.