registerSchema creates some indirection which is not necessary in this
case. newDBSchema can call each of the tables.
Enterprise tables can be added from the existing withEnterpriseSchema
shim.
This adds a new very tiny memdb table and corresponding raft operation
for updating a very small effective map[string]string collection of
"system metadata". This can persistently record a fact about the Consul
state machine itself.
The first use of this feature will come in a later PR.
