feat: Device Functions

Signed-off-by: Darryl Mocek <darryl.mocek@oracle.com>

docs_src/design/ucr/device-functions.md

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+# Use Case Title
+Device Functions
+
+## Submitters
+Darryl Mocek (Oracle)
+
+## Changelog
+
+## Market Segments
+Any segments using EdgeX with device services with devices that support device functions.
+
+## Motivation
+Many devices contain functions that can be called, like the ability to reboot a device.  EdgeX currently does not support the ability to invoke device functions, making parts of devices inaccessible.
+
+## Target Users
+Any users using EdgeX with device services with devices that support device functions.
+
+## Description
+Some devices support functions, invoking some action on a device, similar to a function in software.  These functions unlock important functionality on the device.
+
+## Existing solutions
+EdgeX supports setting attributes on a device.  The workaround for calling device functions currently in EdgeX is to configure a device to call a function when setting at attribute, which isn't always feasible.  For example, to call a 'reboot' device function on a device, a 'reboot' attribute would have to be created and it would have to be set to a value to invoke the reboot function on the device.
+
+## Requirements
+Each Device should have a function resource and its parameters defined to support calling the device function with appropriate parameters.
+
+## Related Issues
+
+## References