LP2012402 Authoritative APIs are optional; disabled by default

LP2012402 Authoritative APIs are optional; disabled by default

Adds a new setting to opensrf.xml called 'uses_pooled_read_replica_dbs'
which controls whether Evergreen enables support for "authoritative" API
calls.

When disabled, the ".authoritative" API variant is simply a clone of the
non-authoritative version.  Similarly, the Angular PCRUD service will
avoid making transaction begin/rollback calls when the 'authoritative'
PCRUD option is passed locally.

Signed-off-by: Bill Erickson <berickxx@gmail.com>