LP#1860703: Create A/T hook and reactor for push integration

LP#1860703: Create A/T hook and reactor for push integration

There is currently no stock mechanism for pushing information out of Evergreen
to trigger activities in external systems.  Third party discovery systems,
among other external systems, would benefit from the ability to be alerted of
changes to data within an Evergreen instance.

This commit adds such a capability by supplying a new A/T reactor module that
can make HTTP requests that supply data to a third party endpoint.

To support the discovery system use case, this commit also adds a new A/T hook,
bre.edit, fired whenever a bibliographic record is modified due to staff
interaction.

Signed-off-by: Mike Rylander <mrylander@gmail.com>