Provide a way to run multi-statement transactions against the system db

[eastlondoner]

Feature description (Mandatory)

CALL apoc.systemdb.executeTx("CREATE USER foo; GRANT ROLE myRole TO foo")

runs multiple statements against the system db in a single transaction.

could take a list ["", ""] of statements or just a semicolon delimited string, whichever is easier or more consistent with other apoc interfaces

Considered alternatives

use a driver application to run an explicit transaction

How this feature can improve the project?

Performing transactions when executing against the system db is extremely useful for making atomic user and roles management changes without breaking things (e.g. splitting roles into separate parts or changing user roles atomically)