Formal policy on new functionality testing [ossf silver]

[bnevis-i]

📚 Docs or Wiki Bug Report

Description [REQUIRED]

OpenSSF Silver Badge requirement:
The project MUST have a formal written policy that as major new functionality is added, tests for the new functionality MUST be added to an automated test suite.

We don't have this today. It is unwritten rule, but we should and it should be added in this area of the Wiki: https://wiki.edgexfoundry.org/display/FA/Contributor%27s+Guide