Add configStem constants

[jim-wang-intel]

🚀 Feature Request

Relevant Package [REQUIRED]

This feature request is for facilitating all services that is using the configuration stem information

Description [REQUIRED]

A clear and concise description of the problem or missing capability...

currently the configuration stem path information is stored in the edgex-go repo. it would be nice to have it in the common library place to be shared for all services. See this section in the PR

Describe the solution you'd like

If you have a solution in mind, please describe it.

add the following constants to the global constants:

        ConfigStemApp             = "edgex/appservices/"
	ConfigStemCore            = "edgex/core/"
	ConfigStemDevice          = "edgex/devices/"

Describe alternatives you've considered

Have you considered any alternative solutions or workarounds?