[CI] [Test] Enforces equal or increasing code coverage in PRs (opense…

…arch-project#1559)

* Utilizes Codecov yaml configuration: https://docs.codecov.com/docs/codecov-yaml
* The purpose of enforcing increasing code coverage over time is to attempt to improve the quality of 
  changes via testing, reduce the need to request tests in PRs, and stay away from enforcing an 
  ambiguous coverage percentage.

Signed-off-by: Tommy Markley <markleyt@amazon.com>

.github/.codecov.yml

@@ -0,0 +1,7 @@
+# https://docs.codecov.com/docs/codecov-yaml
+coverage:
+  status:
+    project:
+      default:
+        # https://docs.codecov.com/docs/commit-status#target
+        target: auto  # coverage must be equal or above the previous commit