ShapekeysToCustomProperties

Takes Shapekeys from a Mesh Object and adds Custom Properties with Drivers to an Armature that allow driving the ShapeKeys from the Rig

Installing:

Download the ShapekeysToCustomProperties.py file.
In Blender go to Edit > Preferences
Click the Addons-Tab
Click the Install... Button
Browse to the .py file and click the Install Button
Locate the addon in the list of addons, it is located in the Rigging Category
Just enter Shape in the filter if your list is very long
Check the Box next to the addon's name to activate it
Done

Using:

Select your Mesh, the one that has the ShapeKeys on it.
Select the Armature that you want to drive the ShapeKeys.
Go to Pose Mode and select the Bone that you want to hold the Custom Properties. Most people use either the Root Bone or a dedicated Properties Bone.
Once you have selected your target Bone, run the Operator from 3D View > Properties Panel (aka N-Panel) > Item > ShapeKeys to Driven Armature Properties