ext: lib: mgmt: mcumgr management infrastructure.

The goal of mcumgr is to define a common management infrastructure with
pluggable transport and encoding components.  In addition, mcumgr
provides definitions and handlers for some core commands: e.g., image
management, file system management, and OS managment.

Origin: mcumgr
License: Apache 2.0
URL: https://github.com/apache/mynewt-mcumgr


commit: 59210e372c927e26637696f2198ff2efe8ea6897
Purpose: Introduction of mcumgr
Maintained-by: External

Signed-off-by: Christopher Collins <ccollins@apache.org>